Stryd: Hands-on with the first running power meter


In December a Boulder based company with only a handful of employees announced that they had put together a running power meter.  They’d taken the same concepts from the cycling world, but moved it into the running world.  In doing so, they’d be the first true consumer running power meter.

For those not familiar with power (in cycling anyway), it’s a metric that normalizes effort expended.  For example, on windy days your pace would be impacted by a headwind (slower), whereas your HR would be higher.  How do you easily compare those across multiple runs?  That’s where power comes into play.  It removes the variables of HR or wind and is one standard you can validate against.  Power is typically expressed in wattage (i.e. 215w), though you often compare different people using watts/kilogram (to account for weight differences).

Of course, there’s been many thoughts and ideas put forth on running power.  But all of these ideas have centered heavily on a measurement device at your shoe.  Such as an insole or the like.  Not with Stryd.  For that, it’s merely a little pod that you clip on your running shorts.

I had the chance to run with it earlier this month, and then get both the raw data for me to poke at, as well as it analyzed by the Stryd team.  Obviously things are still in beta – but this shows you where they are and a bit about their plans moving forward.

The Hardware:


To begin, the hardware is a simple as you can get.  It’s just a little pod you clip onto your running shorts.  Currently the pod has staged an Occupy movement inside what appears to be an old Fitbit Zip rubber clip.  But that’s perfectly fine – it’s a well proven mounting home, so perfect for testing.

The pod itself is effectively not much different than your average modern running footpod, similarly with some accelerometers in it.  In many ways, the magic here isn’t the hardware.  It’s the software.  It’s the algorithms that enable the company to see through all the noise of running and produce something that feels and looks like regular power meter data that you’d see while cycling.

Like most other coin cell battery powered devices, the battery on this should last about a year or so.  For the day I was there it was using Bluetooth Smart, but they also support ANT+ too on the same hardware.  It was simply a case of them working on BLE first because the Suunto Ambit3 supported power meters in the running profile, whereas most other watches don’t.  For example, if you wanted to use it with your Garmin watch today, you could do that – you just need to be in cycling mode (and that it supports ANT+ power meters).  If Garmin were to enable power meters during the running mode, then that’d work just fine.

Speaking of which, you’ll need some way to capture the data.  Right now there’s two options.  The first is pairing to a capable watch.  That would mostly be limited to the Suunto Ambit3 today, again, simply because they left it open to pair to power meters while running (most other companies disabled that to minimize confusion).  But I suspect that’s going to be less of an issue as it’s relatively easy for other companies to re-enable that in their products (i.e. Garmin, Polar, etc…).  Of course, you can certainly use it with a watch using that watch’s cycling mode and collect power meter data that way instead (i.e. a Garmin FR910/920XT/etc…).  It’s just that it won’t then show you things like ‘Pace’, rather instead giving you ‘Speed’.

In addition to using a watch, you can also use their app – which will collect the data and also broadcast out updates in real time using a pair of headphones (wired or Bluetooth is fine).  So it’ll give you real-time stats as you run, similar to most other running apps.


Because they’re using the two standard protocols (ANT+ and Bluetooth Smart) for delivering the information – it’ll pretty much work with any apps that allow you to connect to a Bluetooth Smart or ANT+ power meter.  So you could just as easily use the Strava app as the Stryd app.

Running with it:


When it comes to testing things, the track is a great place to start.  It allows a very controlled environment to figure out exactly how a device works before you take it somewhere more challenging.

After a brief overview of the pieces at play, they got me all setup on the unit.  Getting the unit installed is silly easy.  You just clip it on the back of your running shorts.  At which point you’re done (unless you iron your running shorts, which I probably should consider next time I have a photo taken of my running shorts).


I was wearing two different watches.  The blue one you see to the left is the Suunto Ambit3.  While on the right side I’ve got a FR920XT.  In this case, the 920XT wasn’t doing anything related to the power from Stryd.  It was just along for the run.  On some of the runs they also outfitted me with a phone in a small armband.  This was to demonstrate the phone app capabilities.

With that set, after a bit of a warm-up we had two different structured tests they wanted me to run through.   They were as follows:

Test 1: Interval test of 1-minute hard, 1-minute easy, repeated four times.
Test 2: 10-Minute test sustained 5K pace

The purpose of these tests were to show me how the power would vary depending on what I was doing.  The shorter ones make it easy to see the on/off aspects of running hard, as well as to see the stabilization on each interval.  Whereas the longer one shows a bit of the steady-state pacing aspects.

With that…I got running.


While running with the phone app, it’d audibly tell me my real time stats including power.  Unfortunately I was having a bit of trouble with the headphone staying in my ears – so this part was a bit finicky.  Of course, that has nothing to do with the Stryd system, but rather just the headphones that we collectively had in our bags.  It worked enough that I got the gist of it though.  And, for how the app works, it’s perfectly acceptable.


As I noted to them though, most runners that are running at a level where they’d be interested in power meter data are probably more of the watch (or nothing) type.  So while I appreciate the app, it’s just not something I’d typically use myself.

Next, we move to the watch connected mode.

For that things get super simple and much more comfortable.  One of the data screens had been configured to show power (instant/current), while also showing max power along the bottom.

As I ran, this value would update with my current power.  The harder I ran, the higher the values.  The easier I ran, the lower the values.  What was cool here is that the algorithms they’ve used seemed to roughly jive with power values I’d get while cycling from a perceived effort standpoint.  Whether this was by pure coincidence or mathematical ingenuity is something that probably takes more samples than just me to sort through.  For the most part, when my pace was consistent time-wise, the power values were consistent on the display (there was no wind).


Like while cycling, you’ll see slight variations in power as you run.  Meaning that one moment it might be 258w, and the next 252w.  You can see the above and below photos take a couple of seconds apart with a slight variation in power.  Again, that’s completely normal as you’re putting out slightly different levels.  Most cyclists take care of this by using a smoothed data screen such as 3s or 10s power, which shows you the average of the last 3s or 10s (seconds).


Also like cycling, when you stop, you stop producing power.  You can see it’s now showing a zero value power output.  If I walk, it shows low double digit values instead.


To get a feeling for what this looks like, here’s a short video I shot running around the track.  You’ll have to forgive the camera work, obviously I was trying to hold and run at one time and keeping it steady.  You’re focusing on the top number, which is instant power.

Now, what’s interesting with Stryd is to actually look at something like running up or down hills.  In this case, there aren’t too many hills in Las Vegas proper, so we had to use the very small hill (mound?) near the track – but it was just enough to demonstrate the concept.

Typically if you think about running you’d have a slower pace for the same perceived effort while going uphill.  In other words if you kept your HR the same, then your pace would be lower.  Inversely, if you increased your effort (and HR) you might be able to maintain the pace up a hill.  However, in both cases you tend to get a bit of normal HR lag – and you also tend to have troubles comparing that effort to flat-land efforts.

But how would power work?


Well this is where it’s fascinating and starts to ‘prove’ the concept.  In this case I ran up and down a few times at different paces and intensities.  I was able to clearly start to see the detachment between pace and power, as you would want/expect.  As I ran faster up the hill the power spiked, despite pace significantly slower than on the track. And yet, as I ran down the hill, the power dropped significantly, even though my pace was faster.  That’s because I was putting out far less effort running downhill at pace, than running on flat ground at the same pace.


Between these track tests and the hill I was able to start getting a feel for the concept of it.  Or at least, the beginnings of it.

Just like when you start cycling with power, it often takes months to understand different scenarios and how your body reacts to them.  So I’d expect the same for running.  It’d likely take me months as well to really get a feel for things and really understand what you’re being told and how best to use it.  Still, at least initially the data being shown seems consistent.

Of course, when it comes to racing and training the value will likely be similar to cycling.  People use power targets for different sections of the race, often depending on terrain and the length of the race.  This helps to ensure you don’t go too easy or too hard.

Analyzing the Data:


There is perhaps no better place in Las Vegas to analyze running data than a concrete picnic table on the side of the track.  Unless of course you add a small green metal tea bag container to the table…then you reach scientific geek perfection.  In case you’re wondering, they use that tea container as a portable faraday cage (better than a microwave) to isolate wireless devices during pairing.

First up, let’s just quickly run through the phone app – and then we’ll talk raw data.  The app itself shows some basic stats from the run on the summary screen.  This is of course in addition to the functionality of real-time announcements during the run over headphones.

You can see this histogram of my power during the run itself, along with some summary information up top.  You’ll note that it’s also capturing cadence as well.



Let’s move onto the data recorded though and take a look at it chunk by chunk.

First up is the interval session.  This was where I was doing 4x(1-min hard, 1-min easy).  In this case I had a brief warm-up at the beginning just to get into the swing of things, before I started in on it.  Below is the data shown on their site and collected from the unit.  Note that you can of course use other sites (and I’ll show that in a moment).


For the above focus on the final four bumps, which are the four intervals.  Higher up is faster, lower down is slower.

What you see is that that the red/orange line is power, and that it tends to correlate pretty closely with pace, especially at the beginning and ending of each interval.  This makes sense, especially given the flat nature of the track.  Where you see more interesting data though is when you overlay the HR in there (blue) in that there’s the clear delay as you usually see on HR data (just normal body reaction time).  So while I stabilized pace and power reasonably quickly, HR takes a while to stabilize.

You do see on each instance at the very beginning that my effort spikes as I start each 1-minute chunk.  But despite that happening, the pace actually is still ramping up – a good example of the natural ebb and flow that typically occurs at the start of most intervals.

Next we look at the 10-minute steady state run.  For this we see a pretty solid correlation between pace and power.  It’s interesting to see that despite me being pretty consistent (I was timing each 100m chunk and subdividing seconds per 100m against a known 5K pace), there is still slight variation during each chunk.  This is especially obvious at the beginning, where you see more variation.  Whereas in the middle it’s pretty even.  It’s here that when out on the open road with rolling terrain you could use a power number to pace by (especially in a longer event), rather than straight pace or HR.


Now while the above examples are interesting, I think the most valuable one is actually the small hill repeats.  I ended up doing four runs on it, one the long-ways over the hill (shallower), and then three with variations on the shorter/steeper direction.

First, notice that my HR is pretty much stable across the entire effort – regardless of whether I was going up or down.  Again a good example of HR lag here, and something that’d be pretty common in a hilly race.


Now if you look at the last two ups/downs you’ll see the really interesting alignment there where power follows the hill profile almost perfectly (just like it would when cycling), whereas pace is inverted.  It’s of course slightly hard to see due to the size of the hill, but it’s there.  Now obviously if this were a bigger hill then you’d expect that once your power stabilized (likely as the grade stabilized) that it wouldn’t ‘follow the hill’ anymore, but rather flat-line.


Now in addition to this you can also pull this data into 3rd party sites, like Suunto Movescount.  They had their Ambit3 connected to their account and were able to run through the data during the workout.


Afterwards however they sent me the .FIT files, and from there I could upload it to other sites, such as TrainingPeaks or Sport Tracks.  In the case of Training Peaks I wasn’t getting the exported data to plot (Updated: Found my issue!). Below you can see the results, first on Sport Tracks, then on Training Peaks:



Ultimately, plotting this data is super easy for companies to add since it’s largely already supported by them for cycling power meters – so it’s something that I’d expect to quickly catch on.

Of course, from a large standpoint there’s a lot more analytics that probably need to go on, and ideally on longer runs.  For example I’d be interested in establishing the relationship between cadence vs power, or power vs fatigue.  There’s obviously been a lot of focus on running efficiency, with many companies getting into those metrics.  But this helps to have a more specific data point than just pace (which is impacted by terrain), or heart rate (which is impacted by fatigue).

One final note on ‘accuracy’, and how ‘accurate’ is the system.  Obviously, given there’s nothing out there to compare it to today from a consumer standpoint – I don’t have any method to independently validate that.

Stryd however has gone to some university facilities that have force plate treadmills that can measure power output of runners.  From that they showed me data exhibiting that the unit had near perfectly matched the expensive lab based system.


Of course I have no way of proving if the charts they showed me of near perfection were normal, or if the remainder of the data they collected was more scattered than a game of Twister.  But I suspect that it’s probably at least in the ballpark of what they showed.


Down the road once they release a product – I’ll see if I can sucker find some other university to let me utilize their fancy treadmill and do some similar tests with a couple of folks.

A few final thoughts:


There’s no doubt the potential for running power data will be huge down the road.  Anyone who thinks otherwise is just repeating the historical misbeliefs of people 15 years ago saying cycling power meters will never catch on.  And in the case of cycling power meters the cost barrier has been mostly massive until the last few years (upwards of thousands of dollars). Whereas with this device – their raw materials cost is tiny – with the retail cost in the $150 range.

The trick however to running power will be to demonstrate to people the value of using power over pace (or heart rate), as is done today.  As you can see in my first two examples on flat terrain those correlated quite well.  I’m not convinced in a flat windless race that you’d get a whole lot of additional value from running power than pace/HR.

Where the much greater value is on courses with more terrain, or with substantial wind.  For these power (just like on the bike) can be incredibly beneficial, especially in pacing longer efforts like half marathon or marathons.  Or especially in cases like an ultra through tough terrain.

But perhaps I’ll change my mind on the first part and find it more valuable in flat terrain than I think today.  If and when they send me out a unit to use more long term and really get some good data collected across a variety of scenarios, l’ll be able to make a better determination (plenty of flats in central Paris, and plenty of hills on the edges).

Still, despite all that, for a beta product what I saw is very promising.  They gave me the raw data afterwards – and of course I got to see it myself while it was collecting data.  The results in both cases were consistent and appeared logical.  I would point out that this is an example of a product that appears more mature than most pre-launch products are.  I put this very much in the same maturity level as when I tested the Backtracker system this past summer (who were just acquired by Garmin).  Thus, based on the limited data I have, I wouldn’t hesitate to back them in their upcoming product launch next month.

Speaking of which, here’s the details you’ve probably been looking for.  The dual ANT+/Bluetooth Smart capable unit will sell for $149US when they launch in February.  Right now they’re looking at leveraging crowd funding for the initial lot (i.e. Kickstarter).  They’ll deliver those units in April to your running shorts.

Then by summer they’ll be in regular distribution mode, where you can buy it through more normal channels.  As part of the purchase you’ll get access to the app and their website, though of course since it supports standard ANT+ and Bluetooth Smart power protocols – so you’ll be able to use it on any apps/devices that support that (pretty much everyone).

With that – thanks for reading!  And of course feel free to drop any questions below and I can try and track down answers.


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  1. Tom H.

    Ah…what happens when you run on a regular treadmill? Does the algorithm work then?

    • Yup, the charts are from on the treadmill. :)

    • We tested running on the treadmill and outdoors. We found that running form and therefore power generation varies between the two. It is kind of neat to be able to see the impact of training outdoors vs. indoors.

    • Bert

      Would you be able to elaborate on the impact of treadmill running? I’m currently in a marathon training cycle while staying in an Indian city for work, so I only get to do outdoor runs when I have a bit more time during the weekend.

      I obviously don’t have a Stryd yet, but do have a HR meter and a footpod. Are there any specific changes I could make to my scheduled runs to account for the treadmill effects?

    • When you run on a treadmill, you avoid many outdoor environmental effects, such as changes to surface conditions, wind, and elevation. Adapting to those effects can require changes in form and running power.

      In our tests with Stryd, and when going through the research literature, we found that the same pace can produce different effects on the body when running on a treadmill and outdoors. However, we didn’t find any hard rule about the size of this difference that holds for different runners.

      The following studies give deeper insight on this topic if you are interested to learn more.

      link to ncbi.nlm.nih.gov
      link to ncbi.nlm.nih.gov
      link to ncbi.nlm.nih.gov
      link to ncbi.nlm.nih.gov

      Stryd may be able to help quantify how your own personal running power changes in different running environments to help you adjust your training plan accordingly. If you end up giving it a try in that application, we want to hear about your experiences:)

    • Chris C.

      Hi Jamie,

      Sounds great but it looks like app. half of the articles are not available for free.
      Any way you could give us access to them?

    • Ben

      Hi Jamie,

      Definitely find the “accounting for wind resistance” part of this the most interesting.

      If I worked for stryd, I wouldn’t give away too much of *how* it works, but I’ll keep my eye closely on this spot for when you show proof *that* it works.

  2. Mark Liversedge

    This looks neat. But boy is it going to confuse multisport software !

  3. the5krunner

    Thanks for the heads-up. Interesting. I saw that one of the sports software vendors (sporttracks) allowed a pace to power conversion through one of their plugins. Whilst nice and whilst it could then tie in to a degree with power data from cycling I just couldn’t see how it would be actionable. eg How could you then run in your SWEETSPOT power zone? You just wouldn’t know what the running power was when you were running.

    I guess now there’s a solution. I wouldn’t use it myself but as you say, there are probably many who eventually will.

  4. Trevor

    Quick typo to note: “The hardware I ran, the higher the values. “

  5. Perry Taylor

    I can understand how this takes into account inclines, but how can an accelerometer take wind into account? It sounds like this is much more of an indirect power meter like an iBike than it is a direct power meter like a Quarq or PowerTap, am I missing something?

    • Jeff

      This was my initial thought as well. I wonder if it can tell your rate of deceleration while you’re airborne. I assume you also have to tell it your weight, and to get accurate numbers, you’d probably want to weigh yourself immediately before beginning a workout, since weight can fluctuate so much day to day.

    • Sai To

      I wonder how accurate it can do on different terrain for example dry sand, gravel, muddy?

    • We have a plan to properly account for the impact of changes in wind speed but we don’t have solid testing results on this now. We’ll follow up here, and on our blog (http://blog.stryd.com), when we have more news on this.

    • Takura

      For different surfaces as well as deciding airborne time (to know when to measure wind effect) a connected system of accelerometers on body core and footpods would seem more plausible … but I’d be more surprised if those guys hadn’t thought of that already …

    • Ze

      They won’t (accurately enough for high-level training). This device is assessing power based on essentially statistically associations rather than causal measurements.

  6. GoldRush

    For $150 sign me up. I’d be interested to see how this power data compares to my cycling power data. Possibly a more accurate TSS in Training Peaks like I get with my PowerTap.

    • We found that the cycling and running power numbers for an athlete typically can differ. However, once Stryd has characterized your functional threshold power (for example, with a 5k or 10k run) similar approaches as used in cycling can be used to determine training plans.

  7. Donnie Barnes

    I know you mentioned ultra runners, but to me the thing left out here is how this impacts normal trail runners. There are more and more of us out there who almost never run on anything but trail, even though we are normal folks who shave our faces, eat meat, and only run maybe 20 miles a week. And we some of us even like to geek out on data.

    And for those of us who run on lots of DIFFERENT trails with different terrains, this can help us better identify what kind of work we really did. Especially since our GPS units still lie a lot (yes, even the 920XT shorts me on trail and I know it because I ride the same trails on an MTB equipped with wheelspeed sensor.

    Anyway, I think it’s going to be much more useful in that arena than anywhere else, personally.


  8. Rodrigo Valle Teixeira

    Hi Ray,
    If I understand correctly, the hardware is one (or more) accelerometer, and the magic is all in software.
    Given that you used it cliped to your shorts, the unit was basically static in relation to your core body.

    So….. it seems that the same function could be done by the existing accelerometers on the latest Garmin HRM strap (the one with running dynamics). It would just be a matter of software on the strap and watch.
    Or am I missing something?

    Rodrigo Valle

    • Justin

      I think it has to have more than just an accelerometer. You’d need a barometer for elevation differences, and Ray kept going on about wind resistance, so I would think it would need some sort of wind meter as well.

    • Johannes

      Many watches do have a barometer, too. As for wind, there’s no conceivable way this small unit clipped somewhere on the shorts has any kind of wind meter.

      I’d love for the software to be licensed by Polar, Garmin etc. and incorporated into their watches.

  9. Mark

    If a startup company like Stryd can easily make a dual-band (ANT+ and Bluetooth Smart) sensor, why is it so difficult for manufacturers of other sensors (cycling power, cadence, HR) to also make their sensors dual-band? One notable exception is Wahoo Fitness , but I can’t think of too many, if any, others.

  10. Matt

    Hi Ray, you mentioned that most cyclists use 3s or 10s averages to get a smoother reading, are those rolling averages or set reset averages?

  11. David

    That sounds really cool. For $150 I’ll probably buy one. But I’m wondering how long it will take Garmin/Training Peaks to support running with power. Without those two pieces, it’ll really be somewhat limited. I guess until that time comes, I’ll have to use the app on my phone. Did you mention the phone platforms they will be supporting?

    • iOS/Android, however since it broadcasts on the standards than honestly it can be used on anything that has an app that supports power/etc…

    • David

      Except it is still going to be an issue finding an app that supports power while running. Yes, it should not be a difficult change for any app developer to make. But convincing them that there is a market for it will still be an issue. I think that’s what will hold back Garmin and TP, honestly. It’s not the difficulty in the problem, it’s the perceived market share. Hopefully if the guys at Stryd blow out their kick starter goals, it will show Garmin and TP that there really is interest. (Or maybe could fund some development for those platforms if necessary).

    • My understanding is they’ve already been talking with TP.

      As for Garmin, that’s actually less of an issue with Connect IQ now. Stryd could just develop their own app…and done.

    • Update: Talked with the TP guys and found the issue I was having (it wasn’t showing in preview mode, but is showing in full graph mode). In any case, posted the TP view too. Note that the Stryd folks noted to me prior to upload into TP that at this point the values for TSS/IF/Calories/etc won’t really be correct quite yet.

    • David

      Thanks for the update. Totally going to try this out. Regarding Connect IQ, initially I thought it would suffer from the same problem as the Moxy folks were explaining, you can’t record a custom ANT stream into the fit file. But then I realized, based on their description, “someone” would just need to create an app that utilizes the power meter sensor, and it should record automatically into the file. So yes, that should be an easy to solve issue.

      Just out of curiosity, did you try uploading their file to Garmin Connect? Can it handle power in a run profile?

    • Funny, I hadn’t tried it. But oddly enough, it did import to GC:

      link to connect.garmin.com

      It doesn’t show the map – but it doesn’t on any of the services I use. I think the .FIT file generation they used doesn’t support the map at this time, which is fine.

    • Stryd already supports location information in FIT files. The map will be shown for all the exercises you do with Stryd.

    • The nice thing about power is that mainstream online training platforms already support it, and some have already made it available for running. For instance, we can show running power on Suunto’s Movescount and on TrainingPeaks.

    • David

      Ray, that’s interesting. When zooming in on GC, I had previously noticed that for the first interval, the pace and power change don’t in sync. I had assumed that the power was off. But actually based on the duration of the power bump, I actually think the pace value was off. The power cycles are very clearly on one minute edges. So that initial discrepancy must be due to an error in the pace calculation. Do you know where this pace came from? (GPS phone, watch GPS (which one), foot pod (either actual or emulated by the Stryde)).

    • I don’t know which device this data came from (Ambit3/Phone/Unit itself). I’ll try and get some clarity.

  12. FrostByteVA

    If this really is primarily a software platform, I’d love to see them license it to Wahoo to go along with my Tickr X. Smoothness metrics and power in the same app would be great. I’d still pay $100 just to unlock the software if the Tickr has the required hardware components.

    • Tom

      My first thought as well was whether the Tickr X could be updated to provided the data necessary for the software to work.

      Ray – Do you know if Stryd is talking with other companies about licensing their software?

  13. Pablo

    Great marketing for a foot pod. I was expecting a price range near to the foot pods. I don’t see any added value to what I have right now ( Fenix 2 with HRM-RUN ).

    The work on the algorithms and the software looks very nice. I think the same algorithms can be applied to a cheaper hardware like the Wahoo TICKR X or even from the same data collected by my Fenix2 + HRM-RUN

    • morey000

      “…I think the same algorithms can be applied to a cheaper hardware like the Wahoo TICKR X…”

      or an iphone app. $4.99

      But hey- I paid a lot more for my PowerTap than what they’re asking for this device.

    • A HR strap, likely. A phone might be trickier though due to aspects around you moving your arms as well. Unsure there.

    • peroni

      For android there is an app available claiming to measure power while running
      link to goo.gl

      There is also one for cycling by the same developer.

      Storing the phone is a small waist pack should return similar results.

    • Jeff

      You don’t know how expensive this hardware is because you’re buying it bundled with innovative software. And just because the marginal cost of software is zero doesn’t mean that it isn’t still very expensive in low volume, niche products like this.

    • Ken

      I run with my Samsung GSIII in a Level Flip Belt. No armband necessary. link to flipbelt.com

  14. I have a problem understanding this line of yours:

    “Now if you look at the last two ups/downs you’ll see the really interesting alignment there where power follows the hill profile almost perfectly (just like it would when cycling), whereas pace is inverted.”

    Why would the power rise like the hill profile while pace is dropping. I could see that happening only if you would be accelerating. Or if the gradient would be increasing and your pace would remain the same.
    And i think its not common in cycling that power would increase with every meter climbed.

    I think the “hills” you did were just to small to see where your climbing power would settle and there is too little data to show how this power meter behaves in climbing situations. If you don’t look at time and meters climbed it just looks wrong to me. If I consider short time, that could explain there was not enough time for power to settle in.

    Maybe I’m missing something, but chart and your explanation just don’t look right to me at the moment.

    • As the hill goes up in elevation, my power spikes. On a longer hill you’d see my power eventually settle in on a higher value. Whereas my pace drops, because the hill slows me down.

      Didn’t mean to imply that my power would forever increase. Just that it increased when I hit the hill (which is normal in cycling too, unless you reduce effort).

  15. Nick B

    Single sided power meter= fail

  16. morey000

    want. nay, need.
    The holy grail of run training- TSS!

    Take my money!

  17. Chris

    Do you know what its inputs are? Is it just pace and vertical movement up and down hills? Basically, can it account for wind in anyway, via some measurement or HR based voodoo?

    Also, the pedant in me (and he is strong) thinks that this thing should be called a power.. estimator, or something like that. Even if it happened to be extremely accurate.

    Thanks for the write up!

    • There’s probably some truth in calling it an estimator (similar to iBike). But, until someone comes up with something else in the field for running, or a better consumer-friendly term…I’m gonna stick with it.

      In cycling we can divide things up into direct force power meters (DFPM’s, i.e. PowerCal/iBike) and non, but since we only have one unit in running it’s a bit more…pedant.

    • Grzeg1

      Did you have a chance to test:
      – on a soft surface (sand)
      – pulling a trolley/bike
      – pushing someone in front of you?
      These should show increase of power exerted.

      Great review as always.

    • Daniel

      Exactly what i thought when I read the article.

      What about slippy/muddy ground ?
      How does it change when I am pulling something ?
      How is the differences between carrying more or less weight ?

    • Aaron

      Do you know what its inputs are?

      There is no magic. It’s an accelerometer with a high sampling rate that infers the force required to achieve the (modeled) movement of the athlete in 3D. Right? As others mentioned I’d be surprised if it works on slippery/soft surfaces. I’m less concerned about accuracy pushing people. Unless you’re training for the zombie apocalypse? Or a black Friday sales rush? #smh

      For comparing hills to flat workouts there is already grade adjusted pace modeling (and literature to back it!). Doesn’t seem that compelling. I would need to see a) that there is improved accuracy, b) that it’s useful.

      It seems the value is the “smarts” in pooping out a single value (power) which if normalized to other power training (bike meter) could give you better apples to apples effort values for multi-sport athletes. Better effort values means more accurate multi-sport training load modeling. Which means (in theory) better ability to tune training periodization and tapering.

      (somewhat) side note: I don’t think the “inertia” of the heart-rate based training industry should be underestimated. There are a whole lot of people and companies invested in telling you the ONLY way to accurately measure your fitness effort is by HRM training. They’ll go kicking and screaming allowing an upstart sensor to “proxy” that. Ponder why the HRM market didn’t collapse when GPS watches came out and whether it’s really a question of needing increased resolution of movement sensors and a bit of software modeling.

    • Grzeg1

      @Aaron as it’s hard to get different wind conditions per request, the quickest approximation of head-wind would be some kind of resisting force in front of you. The easiest way to do it is just push someone resisting a bit in front of you.
      This would be just to confirm that the sensor reacts to different power exerted, and not only to hills (they can be probably calculated from 3D accelerometer movement).

    • Richard

      I’m a trail runner and use training peaks and strava where grade adjusted pace is calculated (GAP). In training peaks it calculates much lower training stress values then a same effort on flats based on running threshold values which is very accurate. Same for strava where I can get my heart rate much higher than my marathon pace and calculate GAP is much lower.

      The reason for that might be that my running technique is bad and I jump much more than I should or that the terrain forces you to step in ways that tires the body more. IMO, in all these cases, calculating the weight moved at the hips would be a much more accurate measure of true effort.

      Wind doesn’t matter much at trail running speeds, we often walk or go very slow even elites. Maybe a calulation that takes into account GAP and HR (after removing delay) could provide a power or efficiency value.

  18. Donnie Barnes

    The more I think about it, the more I wonder how useful this might be for other sports like basketball. Ray, have they talked about anything like that?

    Curious more from a training load kind of perspective for guys who play at the college and pro level. Things like RPE are getting more and more common in usage, but this could be something that would really help better quantify the amount of work being done by an individual in that kind of setting (there are some reasons why HR just isn’t good enough on its own).


    • I stopped paying attention to basketball after they moved (my) Seattle SuperSonics to some place in the middle of nowhere…

    • Donnie Barnes

      Hey, I feel your pain on that having lived through *getting* an NBA expansion team in Charlotte (the first Hornets) and then having them taken away when they moved to some city that sits on the coast below sea level. But at least we got them back eventually (and maybe you will, too!).

      But no mention of other sports? I could see this useful on the football field as well. At least for some positions (and I hear you have a team from your beloved Seattle that might just still be playing one more football game?).


  19. Trevor

    Any word on when the company will begin crowd sourcing?

  20. Gary

    This all looks really impressive, but the kind of runner who wants to use something is looking for accuracy otherwise what’s the point? If this device is merely guessing based on variable inputs fed into an algorithm, is this really any more than a gimmick designed to part fools with their money?

    • I think it’s a given that if it’s not accurate, then it’s useless. At this point, according the data they’ve provided it matches. As noted in the post, that’s something I’m looking to be able to independently validate down the road.

    • Justin

      The value is probably more in the precision than the accuracy. Being able to train consistently and then race consistently based on the output of the power is extremely helpful and useful.

    • gingerneil

      I see your point, but as long as it’s consistent, rather than accurate, you can still achieve what you want from it. But I’ve guess you can say this about any power measurements!

  21. gingerneil

    Interesting… I’ve back runscribe, maybe they could build a similar algorithm into their data analysis? They certainly seem to have the hardware, altho now in delay.
    Referring to trails and ultras. How would the power measure be impacted by different surfaces? By that I mean rocks, stones, tree roots etc? Whilst I can see how the measure changes with hills etc, won’t it get uber confused by smaller surface changes you usually face on trails and find it a huge challenge (impossible?) to factor those things in?
    I think I’ll stick to hr to measure ‘effort’ for now…

  22. Brian

    did you mean watts/kilogram in the first paragraph?

  23. I interviewed the guys at Stryd about a month ago and also thought they had something great. Podcast link here – link to zentriathlon.com You did a great job of testing it out for real!

  24. Tom


    Could Stryd’s software work with accelerometers from other locations, such as the Tickr X or even runScribe’s shoe accelerometer?

    Is Stryd talking with any other companies about using their software/algorithms without a shorts-mounted accelerometer?

  25. Donnie Barnes

    I think people are going too far in the “estimator” side. IMHO, using HR data is estimating with a dash of intelligence. This is measuring your actual motion in 3D space in real time and calculating the work required to achieve that motion. And if their algorithms for doing that are verifiable against force-plate treadmills, then it’s not “estimation”, I don’t think.


    • Mark

      Donnie, thanks for this very insightful comment. Your simple explanation of how the Stryd device works makes complete sense. And it also addresses some of the other comments above about whether the device would also require other sensors such as a barometer and wind sensor. If your explanation is correct, then clearly it would not need any of these other sensors – just the accelerometer.

    • Correct. The only thing HR is… is a measurement of your body’s to work, not the actual work itself. Since the reaction is delayed, it’s often too little, too late. But if you’re familiar with what your body’s reaction to known work is (from training), you can keep an eye on the work and never let the reaction happen. If you know that you blow up after doing 250 watts for 2 hours, then you can avoid the blow up by staying at 245.

      The combination of the two is where the magic happens. You learn how your body reacts to specific work, then use that knowledge in races and also to measure improvements to see if a training method is working.

    • atlantis

      Well, what matters is the “measurement of your body’s to work”, to avoid blow up and get the best score possible, isn’t it ?

      This tool could still be usefull but has to be combined with slope, wind, stride (3D ?), HR, posture data to give you hints on your technical mistake of the moment and improve efficiency (because running implies more motion liberties than cycling).
      If not, that is just an “average suffer score” based on weight and some accelerations. I don’t see how that could help improve running efficiency or avoid blow up during a race.

      anyway, I have both tickr run and garmin’s HR+accelerometers strap, just have to wait the first one to implement that kind of “suffer score” around …

    • Paul S

      ” calculating the work required to achieve that motion”.

      But that’s not what you want. Running along a flat at a constant pace, the total work being done is zero because you’re not accelerating so there’s no net force (F = ma). There are other forces operating than the ones you produce with your feet, and they do work, too. What you want is how much power you need to generate with your muscles to offset the power being lost to external factors. Air resistance would be one, but primarily for runners it just seems to be the power lost as your feet convert motion into heat as they slap the ground. On grades, then gravity comes into play, but that’s well understood and the power gain/loss is linear in the vertical speed. But it can’t be as simple as just using the measured acceleration, because most of the time that’s going to be zero.

    • Dylan

      “Running along a flat at a constant pace, the total work being done is zero because you’re not accelerating so there’s no net force (F = ma).”
      I don’t think you understand how running works, it isn’t a constant pace along a flat. Running is launching yourself forward into the air with one foot then landing with the other before launching again over and over and over.

    • Ze

      Acceleration is not a direct measure of the body’s work output.

  26. Mike

    How would you compare this product to the Powertap PowerCal which can measure Power through Heartrate variability? Which would you consider more accurate for running?!

  27. Eric Richardson (Tri Nerd)

    The estimator argument seems short sighted. From what I’ve read, the insole approach has never worked due to the dramatic variation in run form, shoe flexibility, etc. A force plate works in cycling because the drive train is consistent. The “human” drive train isn’t. The only way to measure power is probably from center mass, and if the Stryd people have figured that out, count me in!

  28. Matt

    Just out of curiosity, what would happen if you rode a bike while wearing it? Or asked differently, what force(s) does the stryd measure and how do they differ vs accelerometer based cycling tech?

    • It wouldn’t really work, since it’s lacking being able to create a 3D force profile of your running efforts.

    • Brandon

      I would also like to see what happened if you wore this while riding bike. Since it doesn’t have sensors in your shoes to measure force on the ground could you wear it as a cycling power meter? Would the accuracy and outputs be similar to those from bike specific power meters? If you could wear this for biking I could see this as being a contender in the power meter market with its low price point.

    • Steve

      I doubt it would work while cycling as the gearing and ability to freewheel would make modelling the effort impossible. I assume the model requires that you use muscles to move your mass all the time. That said potentially with Di2 and cadence data you could probably model uphill power based on accelerometer data.

  29. Just wondering what type of power the Stryd is measuring: input (how hard you’re working) or output (how much power is propelling you forward)? This assumes (input power) x (efficiency) = (output power).
    On a bike the comparison might be pedal-based vs hub-based which would have a difference in power based on drive train efficiency. In a running scenario, would Stryd be able to track improvements in run efficiency over time based on a standardized flat/indoor test (for example, a lower power at a given pace)?

    • Great question Kim, hopefully someone will circle back and give an answer…

    • Stryd measures your output power. We compared Stryd power with the power value implied by VO2max testing equipment and found that the two were very well correlated. The output power to VO2max power ratio was approximately 25%, which is in line with human efficiency estimates.

    • Ze

      Great question. It looks like they are just trying to estimate how hard you are working. Basically they have some accelerometer features engineered into an algorithm that estimates a value that is proportional to how hard you are working when running. These values are then collected along with VO2 / HR metrics and matched to power outputs from cycling (or something else with easily calculable power ouput) with the same VO2 values. Then they have come up with an effective “power output” value.

      That’s my general guess. They are not measure positive power generated in the propulsive phase and negative power in the breaking phase. These values would not match power values you would see in cycling.

  30. wdahm519

    Great review. I’m really looking forward to trying this out. I’m glad that the price point for this power meter doesn’t extend as high as cycling power meters. My lack of power meter is due to the exact reason that you pointed out: prohibitive cost for my budget and what I think I can get from that cost.

    Even though there are some meters out there in the low $100’s, my performance gain from that money is better spent elsewhere. At the $150 pricepoint, I can afford to screw around with running power.

    I’m stoked!

  31. Luke

    Would it be possible (likely?) to use Connect IQ to open up the 920 to record power on the run?

  32. Jamwhy

    ~ I used the Wahoo device. I hated it and sent it back. The phone app was terrible.

    According to my source, a person at Stryd:

    ~ This is a high end accelerometer with a very high sampling rate. The trick was to use proprietary algorithms such that the power use is manageable. This makes the hardware different than any other hardware (hardware/software package.)

    ~ This is a complementary device to a heart rate monitor. Though it can be used in a similar fashion as an HR monitor, it can also be used to measure power against heart rate.

    ~ A goal is to adjust stride mechanics such that the power is LOWERED at a given pace. More speed with less power. The breakdown charts can help diagnose the potential trouble spots. My opinion, a “trouble spot” is a subjective thing.

    ~ This is biomechanics modeling. The amount of motion hence energy expenditure is the power used. Whatever caused a higher use of expenditure will be reflected in the power number. For example, hills, sand, wind.

    • atlantis

      “A goal is to adjust stride mechanics such that the power is LOWERED at a given pace.”
      Reinventing running dynamics an N-th time again, with less data this time ?

      “Whatever caused a higher use of expenditure will be reflected in the power number.”
      I your run in deep snow/mud/sand I bet it will be the opposite : you wont get high power number but you’ll definetly get high HR (and you’ll spend far more *real* power/energy into it). Because your efficiency dramaticaly drops. The measure here is based only on gravity center, but it’s completly blind to what your legs are doing to propels it.

    • Jamwhy

      “A goal is to adjust stride mechanics such that the power is LOWERED at a given pace.”
      Reinventing running dynamics an N-th time again, with less data this time ?

      Again, this was what I was told by Stryd.

      I your run in deep snow/mud/sand I bet it will be the opposite : you wont get high power number but you’ll definitely get high HR

      Well… I guess we will find out. The endless speculation becomes a time suck at some point.

  33. Nick Vacirca

    If the magic is, as you say, in the software then do you think they’ll start marketing this as something to sell to other parties? I’m all for getting more functionality out of the sensors all of us are already wearing, but I think we’re really starting to get to a point of redundant hardware.

  34. a_circelli

    Hi Ray. Did you consider a comparison between Stryd and powerCal during running? A few months ago I try power-cal in running mode with my Fenix 2: it works, but I noticed that power value was overstimaded. What do you think?

  35. Brad

    Is that the track at UNLV? If so I have ran around that many a times.

  36. Since it’s “only” an accelerometer on the hardware side and the rest is software. Couldn’t this thing be implemented in heart rate straps in a similar way that running metrics is in the newer Garmin Bands och Wahoo Tickr Run/X? Or is a heart rate strap placed too high to be of any use?

    • Paul S

      It’s likely a much better accelerometer. If an accelerometer is error free, you can calculate instantaneously the current velocity (in 3D) and distance traveled (again, in 3D) simply by integrating the equations of motion with the known 3D acceleration. With errors involved, eventually you’re going to lose track of both, but it may take longer than a typical run to do so with a good enough accelerometer. Of course, the ground is there and you’re stuck to it, so recalibrating in the vertical isn’t a problem.

      So the question is, where are the power losses for a runner? For a cyclist, they’re overwhelmingly due to wind resistance on the flat, and simple mgv (mass times the acceleration of gravity times the vertical speed) plays a role on climbs (and descents). Other causes are minor compared to air resistance on a flat road. For a runner, maybe vertical bouncing plays the significant role on the flats? The question arises because if you’re running at a constant speed on a flat road, the acceleration is zero horizontally, and all you have to do is overcome losses to maintain that speed. (If there are no losses, you don’t have to work at all.) Cycling power meters actually measure the force, and the power is easy to obtain from that. Here, it’s a little more mysterious. They can estimate the power loss due to wind (more or less, since they can’t know the wind speed due to weather all they can do is assume it’s all self generated), but maybe it isn’t that important. So possibly its mostly losses due to vertical motions of the center of mass (the energy is lost when feet hit the ground, turning it into heat). Something to think about when I have some time…

  37. Kevin Weiner

    Power meter for the runner!!!! YES, I use the power function on the treadmill to ensure I am working at the rate I want/ need to ! I actually quit tracking HR since it was easier to plan my runs better on power indoors. I can compare an incline run to a flat run and make sure I am working at my 5K race effort even though I am doing slower hill runs. I would love to see this interact with wahoo ticker I might start using it again. Honestly I am a 6:40-6:20 10K runner in Colorado Springs and due to the elevation and hills everywhere this would be fantastic to know if I am working as hard as should perceived effort only goes so far on various terrain. I will say when I do indoor un, the power is more motivating than anything else. Keep us update because this seem like the grail from a various terrain training function.

  38. Jessica

    This is silly. In running, power (VO2 cost) is linearly proportional to speed. It really doesn’t matter exactly what your power output is, only its proportion to your velocity at VO2 max. This widget doesn’t get you anything new. It’s just an expensive pedometer, and it is defiantly not likely to be accurate enough to be useful.

    • “In running, power (VO2 cost) is linearly proportional to speed.”

      Except when it’s not. Which is hills/wind/etc…

    • Jamwhy

      > In running, power (VO2 cost) is linearly proportional to speed.

      Do you mean V02 cost is linearly proportional to POWER?

    • Even if you take that as true, that would by default also apply to cycling – no? And thus if so, why have a cycling power meter?

      (Playing devils advocate)

    • Jessica

      Which is why when you care, you use a track or treadmill. Or if you live the run by HR dream, you use that. VO2 cost is a measure of power normalized by weight. It is measured in units of milliliters of oxygen per kg body weight per minute. It is a normalized stand-in for energy per unit time (power), except energy is measured in oxygen consumed instead of energy units. Ray, this thing is a pedometer. It can’t accurately measure power. Of course the power to speed graphs look correlated and that creates a nice illusion that this thing does something useful. But the power gaps between 10k pace, 5k pace, etc are only a few percent. The trick is to accurately measure power in a small useful range, not produce correlated charts.

      The gold standard is all the research done by Jack Daniels and his labs more than thirty years ago. Nothing has really changed. This is less accurate and less useful than simply having accurate pacing. I’m a septic and I’m calling shenanigans.

      So company that makes this thing: you want to prove it works? Put a bunch of people on a treadmill with and connect them to a VO2 meter then run them through everything from their easy range up to and even past their VO2 max velocity. Prove the results match for a bunch of people at a bunch of speeds.

    • Jamwhy

      Stryd, like the name states, is about analysis of mechanics. As the makers admit, they used Power as a measurement because it is a single number most athletes understand and can be shown in realtime on a watch. In reality, there are several components to the stride that can be shown. I think, perhaps, you are conflating the idea of effort with speed. This is a notion from the outdated concepts of the old coaches, such as Jack Daniels.

      The new coaches came about almost a decade ago and talked of mechanics. They are ridiculed to this day yet their ideas press on. Pose, Chi, Evolution methods were doing minimalist footwear before Born to Run came out. Now, I am seeing some of those mechanics ideas becoming mainstream which is wonderful. Long ago, the Pose Method forums would go on about the physics and mechanics of running efficiently ad nauseam. Now the technology is allowing us to analyze what we once speculated. This is could be a book to these methods of teaching.

      Jack Daniels told people to run a race then train against that race time. He collected enough data to come up with a heuristic. I didn’t read any sort detailed running mechanics in his famous book. Even today, people like Pete McGill say these running methods are fads in his new book. Running form is self-selected, he states. I say wonderful and these old fuddy-duddies can stick to their old ways. That means it will be easier to beat their products :)

    • I’m not entirely sure why one would say it’s a pedometer. A pedometer tracks steps, that’s it. Over the last few years that’s expanded to tracking distance, perhaps even stride length, but that’s quite different than this. This is mapping your movement in what is effectively a 3D world. I’ll try and get the OK to show some of the 3D stride mechanics images they sent me capturing what is shown every footstep taken. Interesting stuff.

      The reason HR isn’t always a good proxy is the same reason it’s not within cycling: HR is very much subject to a number of factors – most notably fatigue. Now one can debate the merits of racing and training trying to account for fatigue – but it doesn’t change the fundamentals that HR is impacted by fatigue (or sickness, etc…). For example, oftentimes after a redeye flight if I go and do a long run immediately I’ll have astounding pace to HR ratios – with my HR typically 5-7bpm lower than normal for that pace/terrain. The same is often true when an athlete is exhausted.

      Now – there’s plenty of valid debate to happen down the road in terms of how power can be applied in running. Whether or not it’s accurate in X, Y, and Z conditions. Or against A, B, and C people. But, it’s seemingly silly (or premature) to write off a technology simply because one doesn’t understand it. If that was the case, then we wouldn’t have a lot of technologies we see today in sports technology.

    • Ze

      VO2 measures the aerobic cost of the activity. It doesn’t catch the anaerobic component.

      If you start sprinting, your VO2 values won’t reach steady state for ~ few minutes. You’ll totally miss the hard work that started almost instantaneously when you started sprinting.

      Secondly, VO2 measures the human energy cost, but not the gross mechanical demand. Ideally this is what a power metric should capture. Then, you should be using both as a better assessment of running economy.

      That being said, I think this device can do some fancy stuff, but is inherently limited in that it is accelerometer-based and thus just won’t be able to extract causal power-generating metrics.

  39. Keith

    If they were able to do this akgorithm without anything to your feet, what would stop/prohibit them from combining into a bike powermeter? Then some app developer could build something on the new connect iq. Granted this is simplifying it, but if it could be done for running, why not biking?

    • The key difference is that they’re measuring movement on the body. In the case of your bike, that movement would have to be measured at the feet, and since in that case you have a platform between you and the ground (the bike), you can’t make the same assumptions about your relationship to the ground.

  40. Ioannis

    since it tracks movement dont you think that garmin is half way there with running dynamics?

    • In my mind, what Garmin has done is ‘interesting’, but not terribly useful. I’ve yet (almost 18 months later) to see any actual relevant way to apply GCT or VO metrics to improve training or racing.

  41. jbenjamint

    Regarding accuracy – you could find a long hill with a gradient over say 15 percent and 500m vertical climb. Use this power metre and also calculate power from first principles. That would show whether this is truly accurate power.

  42. azan

    Did you try and correlate the power measurements with what you would get at comparable “effort” on a bike with PM?

    • It’s tricky. In some ways I found it compared well, but in others less so. In general, most people have different HR zones for running and riding. I’m no different. It tends to be much harder (at least for me) to put out a higher HR while riding than running.

      To that end however, the perceived efforts seemed to be in the ballpark. So those 250w sections sorta felt a bit like what 250w might be on a bike. Not a perfect alignment, and also a bit skewed by just the reality of CES (fatigue/tons of walking/etc..).

      For me personally, I’d really like to be able to just have a unit for a few months and start collecting data and getting a bit better feel of the system. As other shave noted, it’s a bit hard to develop complex thoughts about it on just a few short runs.

  43. Chris O'Brien

    As in cycling meters… One of the things I’m interested in is the balance between legs… seeing as this goes on the shorts, it seems that there is no capability to see if Ol’Righty is putting out too much power and Lefty is getting a free ride…

    • Aaron

      Interesting point. I’m trying to visualize what unequal power output would look like in a runner, since the legs are connected to the ground and not an intermediate power train. If power on one side is consistently higher, the runner would (frustratingly) run in circles, no?? Obviously ridiculous!! :) Instead would you expect some unequal wobbling stride/hobble/limp? Which should be reflected in a periodic ground contact time and/or vertical oscillation. Assuming we could get those sampled at a per stride frequency.

      An extreme case – hop around on one leg. Do we need to measure power to detect this, or can we do it equivalently via body movement.

  44. michael gross

    Wow! A very interesting review for sure. The question will be how to utilize the data as runners are not used to this type of analysis..

  45. Jason

    Would it be possible for Garmin to update the current watches on the market to have a power option while set to running?

  46. michael gross

    A very interesting review for sure. The question will be how to utilize the data as runners are not used to this type of analysis.

    • panos

      1. you do a test to find your hr threshold and at the same time measure power.
      2. you divide your hr threshold power to zones.
      3. you train following power zones not hr zones.

      Of course if you train on flat surfaces this gadget is useless because pace/speed are more useful in that situation

  47. Troy

    Did you do any testing against wind resistance on a flat track. I could see how they could calibrate a model indoors on a treadmill to seem consistent for given slopes/gaits, but a good test would be say to run both directions on a windy day on a flat track and compare heart rate and perceived effort against the power numbers it puts out for both directions.

  48. panos

    I don’t think there is much more than basic physics.

    Suunto could build an app to show running power and there are one or two allready created by users.

    I have also created an app to measure power using basic physics formulas and i will test it next week.
    Maybe the data i get are not precise, but as long as they are CONSISTENT i should be fine.

  49. Laurent S


    Could you try to upload the data (coming from the Garmin) in Strava? and try both ride and run mode?

    Thank you :)

  50. Oskar

    You can actually change from speed to pace easily on the 910xt in the menu. Back on Garmin Connect you can then just change the workout to running instead of biking (or whatever it’s called in English). To get an accurate current pace based on cadens while having it in bike is another thing, guess it just won’t work.

    Do you think Garmin will update the 910xt to be able to show power during a run or has Garmin forgotten the 910xt users by now?

  51. GS

    I like the idea! I’d enjoy having an estimate of running power on a flat smooth asphalt road in running shoes, and compare that to a barefoot dune/beach run with hills, mud and sand. The more metrics, numbers, spreadsheets and statistics, the better.

    And I’d certainly try out what it would register for footbiking. It may not be designed for that, but it would allow display of a realtime figure, and allow for a quick comparison between sessions (now it is something I can only compute out of HR+speed+foot pod data afterwards).

    No bike power profile on my Fenix 1.. but I hope that lots of folks sell their Fenix 2 when the Fenix 3 becomes avaliable.. ;-)

  52. Sebspi

    Can this be used in other sports like skimo or cross country skiing ?

    • Paul S

      Almost certainly not. The primary force opposing the motion of a skier is the friction of the skis on the snow. That’s pretty variable, depending on waxless vs. waxable, how well you’ve waxed, how deep the snow is, whether you’re breaking trail or not, etc. There’s not likely to be a model of that (if one could even be made) in the device.

    • Sebspi

      Thanks: that’s what I guessed… I did not read the whole post to undestand howcome it can generate an actual wattage, just being stick on your back, even just for running…

  53. andrew

    For someone who does a significant amount of hill running wearing a weight vest. I’d like to see if there is any use for this product to see how much power is going out at different loadings, grades, and paces.

  54. andrew p

    For someone who does a significant amount of hill running wearing a weight vest. I’d like to see if there is any use for this product to see how much power is going out at different loadings, grades, and paces.

  55. Long Run Nick

    I wish I would have paid more attention in my high school physics class 50+ years ago. Love the discussion. Who would’ve thought something as simple as running( something most of us did before we actually walked) had so many facets? I am sure the Kenyans use all this stuff, or do they?
    Ray, again you rule.

  56. Christian Köhler

    I still ask myself: What does Watt really mean when running?

    Yes, it is a very meaningful number in the bike. Unless there are extreme conditions (wheel looses traction on an icy road) or your bike is in very bad condition the watts you push onto the pedals and the watts that push you forward are nearly identical. A road bike in decent condition has an efficiency of some 98 or 99%.

    This is not as simple when running. Efficiency (how many percent of the watts you push into your feet do actually push you forward?) can be very different depending on technique and other factors. When running in place, effiencency is actually zero. What does the unit show in that situation? Does it show the 250W that make you tired or does it show zero because you are not going anywhere?

    Of yourse we are not running in place during a race, but I don’t think running efficency should be assumed to be constant. Towards the end of a long run (marathon) it will be much worse for most of us.


    • Running form has direct impact on running efficiency. When we run, we push our body both upward and forward. To improve running efficiency, it is wise to reduce vertical bob to minimize the upward effort. Meanwhile, try to avoid overstriding. Otherwise, more forward effort is needed to compensate for the braking force. Towards the end of a long run, we are tired and our running form change, so does our running efficiency. Stryd is able to measure these effects and provide feedback to runners to improve running form hence efficiency.

      When we run on treadmill, our body moves forward relative to the treadmill belt. The efficiency definition is the same as running outdoors. On the other hand, we found that running form and therefore power generation varies between treadmill and outdoors. It is kind of neat that Stryd is able to see the impact of training outdoors vs. indoors.

    • Ze

      Hi Jamie,

      “To improve running efficiency, it is wise to reduce vertical bob to minimize the upward effort.”

      This if false. Respectfully, this comment indicates Stryd does not fully understand biomechanics.

      Sincerely, a PhD in biomechanics.

    • Bachoo

      Perhaps you could expand on this Ze?

      Sincerely, a PhD in school of life

    • Paul S

      I’m not Ze, but my PhD is in physics, so I think I can guess the answer. We (and by “we” I mean people who run regularly, not me) probably run pretty much as efficiently as possible already, with improvements possible only at the margins. Hominids have been running for a long time, and if it were possible to be more efficient moving ourselves, we’d already have found the technique and used it. If you deliberately try to decrease the vertical bob, because of the way legs/muscles work mechanically you probably decrease the efficiency and increase the wasted energy. After all, whenever we can we do things to make self powered movement more efficient (skis, skates, paved roads, bicycles), and this would be no different. But I’d be interested in what Ze has to say as well if he’s still around.

    • Correcaminos

      Reportedly, Mo Farah had to work on reducing his bouncy stride, to develop a more efficient stride for running marathons. He may not have won one, but the improvements have carried over his return to track, to impressive results. You can easily see the changes by comparing his form before and after.

      Movement not only in sports but say, while playing an instrument, can be fine tuned for efficiency for a long time before we can say “we probably run as efficiently as possible already”.

      I think the Stryd can be an exciting development in this respect.

    • Ze


      Paul S gave a pretty good response.

      I speak in general, but it is based on specific knowledge of how the body is oriented when interacting with external objects.

      One specific example – wheelchair propulsion. Just like running, one could if you want to improve efficiency when pushing a wheelchair, you should just push so that the force is tangential to the wheel rim. But this does not consider the biomechanics of the upper body – a tangential wheel rim force creates a large moment arm about the shoulder and requires more muscular effort than other force directions.

      Point being, individual biomechanics matter. And before you attempt to change them, you really need to understand what the heck is going on. Like, if I just try to reduce bounce, I’ll probably become less efficient. But what if my dorsiflexion ROM increased 10 degrees, then maybe…

  57. ekutter

    I suspect this will be kind of like Garmin’s running dynamics. It is a piece of information, probably interesting, but is it useful? Maybe combining multiple pieces of information like this and the running dynamics will help answer Christian Kohler’s questions. Garmin’s HRM Run could probably be adapted to provide most, if not all, what this provides. I would expect it to take awhile for the science to make real use of the data. I also would think some kind of direct force measurement (like in the shoe sole) would be needed to make full use of these numbers.

  58. Ben

    You write, “Where the much greater value is on courses with more terrain, or with substantial wind. For these power (just like on the bike) can be incredibly beneficial…”

    Have you confirmed this with the company? I am very skeptical. How can they know that there is a headwind, say, if you run the same way (so the pod has the same movements)? I don’t think they can.

    An easy test would be to run back and forth on a straight stretch on a windy day. Keeping the same pace, does the power go up/down when you are running into/with the wind?

    I am also a bit skeptical (although less so) of the treadmill test. I am curious if it gives the same power levels for running flat at the same pace on and off the treadmill. And ditto for running uphill on and off the treadmill. I think it would be difficult for them to make these power levels match. The issue of consistency on/off the treadmill is not really very important to me—I only want consistency off the treadmill. However, if the power levels on/off the treadmill are inconsistent, then their testing procedures are flawed, so there could be other problems as well.

    Finally, I am not as optimistic as you about Garmin and Strava updating to incorporate this information. It’s a chicken-and-egg situation. They aren’t going to update quickly if few people use these units, but few will buy these units without their support. Maybe Stryd can make a deal to get this going.

    • Yes I’ve confirmed it with the company. After publishing they also validated I didn’t misstate anything in the post.

      No doubt, I’ll do lots of testing once it’s available – and this is just a small preview of where they stand pre-release.

      As for Garmin & Strava incorporating it, I don’t see any issues there. Devices that support Connect IQ can already incorporate this with the release of apps (by 3rd parties). So that’s taken care of. And Strava supports it within the cycling profile, so it’s really just a case of enabling that metric to be shown on the running profile (since it’s already recorded).

    • I share Ben’s concerns. A pod at the back of your running shorts can’t sense wind so at best they’ll have to try to separate a headwind from running at an easier pace by changes in leg speed or something.

      The concept they’re using can and has been done in cycling. The reason the names of these companies don’t spring to mind is that they’re long gone and they were never taken seriously when they were here.

      Ray, you’re spot-on when you say power is coming for running (and other sports) I’m just not convinced this is it. I’m looking forward to your longer-term testing!

  59. Thomas

    I’m also very much into power/watt training for running (I have a powermeter on my bike). However where it becomes a little uncertain in my perspective, is that a powermeter on a bike, is a measured effort. In this Stryde sensor/pod, the only way I can see it’s done, is a calculated effort. It may be good enough/precise (threadmill test shows good signs). However I still think we need to see what the masses think about it. Does it work in all the different circumstances, wind, hills,running form etc.

  60. Paul S

    OK, I realize now one of the things that’s been bothering me about this. “where power follows the hill profile almost perfectly (just like it would when cycling)”. No, it wouldn’t. On a bicycle, you crest a hill, and (assuming a hill worthy of the name) your power would drop to zero immediately after cresting and beginning the descent. In no way would it follow the contour of the terrain. Runners aren’t cyclists, and you have to keep your feet moving underneath you and control your descent, but I’d bet money the same thing should happen, the power output should immediately drop to low levels as you headed downward and gravity (rather than you) provides the energy needed to overcome whatever is resisting you.

    Incidentally, the fact that power goes up while climbing is a psychological reaction, not a physical necessity. Physics says that you need a certain amount of energy to raise your body vertically a given distance, but doesn’t say how fast you have to generate it (power). If you maintain a constant power, you’d still make it to the top, just slower (on a bike you’d have to stay upright, though). We work harder on climbs because we want to get it over with and we don’t want to go that slow, not because we need to.

    • Yeah, I need to tweak my wording a little bit there to make it more clear – but yes, it would ‘level out’ as the hill levels out. If you look at the first hill you can kinda see that. I took that one the long ways and it shows up. Obviously, it’s just too short to make it super obvious in the graphs.

      (Funny, on my ride today I rode up the longest hill in Paris – a touch under 2 miles long, but rather painful (link to dcrainmaker.com) – kept on thinking how perfect it’d be for Stryd.)

  61. Gabriel

    No L/R measurements!!??

  62. mucher

    Just wondering if – for the sake of legacy support – they couldn’t make the Stryd register as a foot pod/cadence sensor – not sure if there’s an upper limit on cadence, but I think it would be in the ballpark of max power and it’s already supported on all the major platforms.

  63. Sorry just had to ask. Can you do static load test with it ;)

  64. Till

    Forgive my skepticism, but I fail to see what this device can do that would not be achievable with a GPS, heart rate sensor and accelerometer, all built in to a watch, and some clever algorithms that take into account parameters such as maximal heart rate, body weight, etc. The only advantage I see here would be a measurement of acceleration of the centre of masss, independent of relative arm movement, but if that cannot already be accounted for, a second accelerometer (such as in a foot pod, or indeed one clipped to the shorts should do the job). Is this all there is to it?

    • Fenix

      Does such a thing exist though ? And if it did – wouldn’t it be far more expensive than the cost we are talking about here.

  65. Matt

    Hey Ray and Jamie from Stryd,
    Being that the Forerunner 620 is not compatible with Connect IQ, would Garmin still be able to just open up another channel and record the data to the watch? Or, would the software on the 620 need such a considerable reworking that it would be unappealing for Garmin to spend any time/money on making the Stryd work with non-biking or IQ compatible watches? I loath running with my phone and would have less interest in this cool product if that (or some other new watch) was the only way for me to capture the new data.

    • Pretty unlikely on the FR620 unfortunately. Stryd could technically broadcast power on another channel that the 620 understands, like HR or cadence. But HR typically has a filter cap in the 250bpm range, and I don’t know if cadence has something similar.

    • Aaron

      For storage: Cadence and Heartrate values are represented in FIT files as 1 byte. The protocol allows arbitrary definition of data value size within the file. So…. technically you could record samples > 255 into the records called “heartrate” or “cadence”, but I have to think there are thousands of software apps out there and probably garmin firmware hardcoded with assumptions these wont exceed 255. I don’t know about the broadcast protocol limits.

    • John Friesen

      What about the Fenix 2? It obviously supports power.

  66. Brian

    I would buy this upon release if I knew it would work with my Garmin Fenix (or 405 or FR60).

  67. As an ex long/triple jumper I just wonder whether the metrics could actually be used to estimate the power generated on the run up and also take off? To me it looks as though it could be a very handy in all sorts of athletic events. I’m sure with a bit of work on the software side it could be able to monitor angles of take off, track forward rotation etc. it would be great if the developers allow the device have an open platform in which others can create apps.

  68. amadeus303

    Ray – can you clarify… are there already ConnectIQ apps that allow for Stryd to be used with a running profile?

    If not, could one create a custom profile to make it work?

    • Within the Connect IQ world, there are basically four types of ‘things’:

      Watch Faces
      Data Fields

      To date, only Watch Faces and Data Fields have been released. With Apps and Widgets forthcoming shortly. That’s really where you’d expect to see the Stryd functionality enabled.

      That said, I will note that the FR920XT does actually connect to a power meter in the running mode. It just doesn’t record that data at this time. I know this mostly because the KICKR broadcasts power 24×7, and when in the proximity of the treadmill where I’m doing my runs, it picks it up. But nothing is ever logged from the KICKR (it would at least have logged a zero-power value).

  69. BoscoK

    This will be even more handy if they can get it to measure power from both legs independently.

  70. Steve Sirois

    “As I noted to them though, most runners that are running at a level where they’d be interested in power meter data are probably more of the watch (or nothing) type. So while I appreciate the app, it’s just not something I’d typically use myself.”

    …except for the cyclists who train using TrainerRoad where most of them use a display like a monitor or phone/tablet to see when they need to change their power output. Until someone comes out with a Google Glass type display for sunglasses, having an audible note to increase your power while running should be beneficial instead of having to look down at your watch to see if you’re hitting the right power numbers.

    Thanks for the nice sneak peek at a promising new device that might have potential at changing the running world!

  71. Gary Gellin

    Someone sent me a link to the “RPM^2” shoe insole power measurement device. It’s hard to tell exactly what it does or how it works from their web site, but it seems to me that it could be a better approach to measuring power on varied terrain and conditions. Ray posted to a comment thread last August that he is familiar with it but hasn’t tested it. Any update???

  72. sebspi

    using a FR310XT, it would display the power values in cycling mode, is that right?

  73. Anthony

    Just wondering if any of the early adopters have received their stryds?

  74. Marathon Man

    Are you able to share how Polar plans to address Stryd in its future products?
    Are they even considering incorporating the ability to connect to Power meters in their running profile?


  75. Julio

    Have you had any updates on these guys? I wonder when we can buy one. Do you have other inputs from other running power sensor products? Have you looked into link to rpm2.com ?

    If the sensor is based on accelerometers, then with a software update, a watch like the Ambit3 should be able to measure running power already, don’t you think?

    • They were saying in the last update that probably August for shipping.

      I have looked into RPM2, but it’s really not what they make it out to be. The app is highly proprietary and really more about medical use than sport stuff.

  76. Jason

    Hi Ray,

    Question, don’t you think Garmin could create a comparable algorithm off of the HRM RUN data. Obviously it’s not on the small of your back, but it’s an accelerometer directly on your sternum. Wouldn’t seem to take much to “correct” for that difference, unless I’m way off base. Just curious, or someone with some programming skills could make a Connect IQ app and sell it for cheap * high volume = easy money.

    • In theory it might be possible. But at the same time, I’m not deep enough in the precise reasons why they selected what they selected. Meaning, I’d have guessed if you could do it all within a chest strap, they might have gone that way.

    • Marathon Man

      I thought Stryd had decided to ship a device that was worn on the chest instead of the clip on design that you tested. Pretty sure I saw an update where the device would be attached to a chest strap and measure Heart Rate and Power. Am I wrong here?

    • Valid point, indeed, I missed that update. Bummer, I much preferred the clip-on version. :-/

  77. There have been mo updates to their blog since July – and even then, it all seems to be marketing hype but no solid information as to the progress of the unit and when it might be shipped.

    On the Stryd forum, some people who paid for the early bird subscription have started complaining that they have no information and that they have not received emails.

  78. Glad to hear that. The posts I looked at were four days old. I didn’t see anything more recent than that.

    I’m surprised that they aren’t more open with their announcements.

  79. Whoops – didn’t go into a quote box

    Today, we are thrilled to announce, we are getting ready to ship 360 Stryd devices to our 120 Super Early Bird Coaches this coming week! Earlier today, we received the 360 shipping boxes for Stryd. The only thing we are waiting for is the chest strap, which will arrive this coming Tuesday. Then, Stryd will be on its way to you.

    Thank you very much for your patience since the first day of our Kickstarter campaign. Today is a beginning — From the day you receive Stryd, we will be working with you to establish power-based run training methods. To this end, we will launch the online training center this coming Monday. Please expect an email then.

    If your address has changed since placing your order, now is the time to update it through Kickstarter
    (link to stryd.com).

    For the rest of the 1000 Kickstarter backers — Everything is on track. We will have the devices ready by the end of September.

    Looking forward to working with every one of you!


  80. I’ve received my Stryd Early Bird device. So say I’ve been excited has been an understatement. The moment I returned to work and found the box, the rest of the evening plans went out of the window, and I was out for a run!

    Based on that first run, I’ve written a brief preview of my production device on TitaniumGeek.com. Its going to be quite an interesting learning curve, over the next few weeks, and looking forward to the Stryd Coaching!

    Here is the direct link if people are interested

    link to titaniumgeek.com

  81. Seems like they should just display your real time normalized pace (what your pace would be if it was windless and flat) and IF (% threshold effort) instead of watts to make the data more easily understood by the average user.

  82. Cheryl Weeks


    After reading your review I am interested to know if I wore my Cycleops HR power meter strap for running as I do for riding, whether the data would be comparable to that of the Stryd? After all, it also works on algorithms although I realise of course that you would get the coaching cues…

  83. Anders Risager

    Not sure about this, so maybe you could clarify Ray, do I need to invest in a new watch (as I currently use a Vivoactive as a day to day watch but I also have an old Fenix 1), to use the Stryd or can I for the time being, use my phone (Nexus 6) and their app to get live power data while out running?

  84. Robert

    Thanks Ray for making me buy this thing called Stryd :) Will you, as soon as so got yours, undertake another review? Maybe you can use your Connection to get Garmin to open up the power channel for running. Like always, appreciate your work and effort!

    • Yes. I got a pre-shipping notification last night, which hopefully means it’ll ship out today and maybe I’ll have it mid-next week. Once that happens I’ll probably test it for about a month getting the hang of it.

    • Bill

      Following. Got mine today but just had meniscus repair. Will be a while before I can try it out. Curious to know if it is producing power reading independent of HR.

  85. Sebspi

    I just got mine tonight! So tomorrow first tests!!!

    Ray, what kind of testing protocol do you plan? I’m planning some kinds of long and short uphill intervals, a Vertical Kilometer of sort of…

    • A very varied one. I even bought a nifty wind measurement device (finally had an excuse for doing so).

      But here’s roughly what I want to cover:

      1) Intervals
      2) Intervals into/with direct head/tail wind (preferrably sorta strong)
      3) Running on trail/hard surface differences (I’ve got a little loop that’s about 400m long, half concrete, half dirt)
      4) Running up/down hills
      5) Long run variations

      I’m sure I’ll come up with more. But really a lot of my focus will be on validating whether or not the unit can pickup changes that would impact power (such as terrain or wind).

    • Joe

      Does the device “need” to measure heart rate? I am curious if you intentionally block skin / electrode contact if the “power” measurements are affected.

    • There are these training resistance parachutes. You could attach it to a bike to see power increase needed (defined speed) versus no parachute. Then you could check the difference between parachute and no parachute while running with Stryd. The results at same speeds should be similar I guess ?

    • That’s an awesome idea. Off to Amazon to buy a parachute…

  86. Tatiana

    Thanks for review! Got mine, not tested it yet… One question, as far as I understand the activity mode for FR920XT should be “bike”… Can I change it later in garmin connect to run and still see the power?


    • Sorta. You can change it on Garmin Connect, but it won’t still show power (unless something has changed). Kinda a pain.

      (Suunto does still show it however)

    • Chris

      Just for anybody that might be reading – the process is working fine with Polar V800 and Flow. I setup a seperate bike profile that uses my running zones for HR/Speed. Sync the Stryd with the V800, go for a run/ride and convert to a run afterwards on the Flow website. All the power information stays intact.

    • Sebastien SPIESER

      you can change the sport type on GC, it will still keep the power values; see: link to connect.garmin.com

    • Tatiana

      Thanks, Sebastien! I shall try to

    • Mark Acher

      Sebastien – Thanks for sharing the data. To understand, while recording the effort, your device was in cycling mode. Then, after your effort was uploaded to GC, you went in and manually changed it to run. Please confirm.

      If the above is correct, what do you make of your cadence data. I’m having trouble understanding what went on there as the data doesn’t seem to comport to either running or cycling. Is that data strangeness an issue of relabeling the effort within GC?

    • Mark

      I think I have answered a lot of my own questions via the Stryd device support page.

      Link: link to stryd.com

    • Sebastien SPIESER

      Hi Mark,
      OK you may already have the answers then!
      But yes, that’s the way I did in Garmin Connect.

      For the cadence, lots of posts on that topic in Stryd Forum; seems Stryd gives a SPM value to the watch, while a footpod gives a RPM… GC simply doubles that value…

    • Bill

      Thanks for working all this out. It will be a couple of months before I can try it as I had knee surgery. But I am following your posts on this as I also have a Garmin 920XT – and I was not thrilled that I might have to use it in cycling mode because my data gets uploaded from GC to Training Peaks for my coach.

      When I went to the link you provided above I note the following:

      Garmin 920XT, Fenix 3

      Supports power and heart rate.

      1. Note that power is supported in the cycling mode. Note that you can use the Stryd Garmin IQ app to show pace in the cycling mode.

      2. To show power in the run mode, please connect Stryd with the watch as a foot pod. Stryd will be displayed in the cadence field on the watch screen while running.

      So I am taking that as an either/or – either (1) you use it in cycling mode or (2) you use it in run mode and connect as a foot pod.

      So the second option sounds better to me – am I missing something there? For instance, when you say ” Stryd gives a SPM value to the watch, while a footpod gives a RPM… GC simply doubles that value…” does that mean that by using it connected as a foot pod that my data would be off by a factor of two?

    • If you use the 2nd option you don’t get power in the right field, so it’s wonky. For example, if you look at my Strava files the last few days, I did that and things are all amok there.

      Basically, Garmin needs to simply enable power recording in running mode (like Suunto does), which instantly solves it all. I think it’d be fair if they did that on their Fenix3/Epix/FR920XT watches (since it’ll happen anyway early next year with Connect IQ recording). But also, I think they ought to add it to their FR630, since that actually makes it compelling for two groups:

      A) The tiny % of people running with power
      B) Cyclists who want a super-small watch that can record power


  87. Jonathan G

    Could you pair with an Edge (eg, 500) and wear that on your wrist? Power would use the power channel, pace would be speed, etc…, would running cadence show up in the cycling cadence field?

  88. What principle is the device using for measuring power – in other words how does it operate without giving away any secrets?



    • That is a big question which is being asked in quite a few places. There is a debate about this on the Garmin forum as well

    • Accelerometers (and I believe a barometer for altitude, given the vent on the back), plus some math.

    • Paul S

      If you look in the comments above, you’ll find out what’s involved. Briefly, one way is to make a model of the forces that are on a runner. From that model and the accelerometer you try to extract the force(s) that the runner is producing with their muscles, and thus the work/time (power) that they’re generating.

      The Stryd has (as far as we know) an accelerometer, an altimeter, and a HRM. HR is loosely related to power, so they could just use that (or use it as a check). An accelerometer can in principle give you position and velocity by integrating the equations of motion, but I’m sure consumer level accelerometers pretty quickly get swamped by error in doing that. (“Dead reckoning” using an accelerometer is used to navigate nuclear submarines on a global scale as I understand it, but I’m pretty sure the captain or navigator doesn’t wear it on his body.) An accelerometer will give you total force and incline (how well, I’ve no idea).

      But this brings up another way Ray should test the device. Ray, you should definitely take the Stryd out on a bike and in a car. The power numbers would be worthless, but it might give some insight into how it works. On a bike, vertical oscillation should be near zero, and the speeds much greater, so you can see whether it’s taking wind resistance into account, and how well the power up and down works out. In a car (or in the Metro), you’re not working at all, but it’d be interesting to see what the Stryd says.

    • Fwiw, they commented recently (like two days ago), that they aren’t using HR at all. That’s logical, given their previous units were not HR straps (and they’ve said they plan to release those variants down the road).

      As for riding, actually just did that last night on the city share bikes. I uploaded it to Strava, for those that are curious – titled Veliber Home.

    • Paul S

      That makes absolutely no sense at all :-) Power spikes correlated with deceleration. (For that matter, why does it show any power at all?). There seems to be some weak correlation to heart rate, but of course you would expect that if it were actually measuring power. How were the roads you were riding on? Velibs are big, heavy things, right? Do they have any suspension?

    • Roads were mostly paved, with some cobbles sections with a few shifts in grade (up/down onto grade-separated tracks/etc…).

      The Velib has no suspension, but is about 20-22KG. Beasts.

    • Ze

      The fundamental concept being used is likely Force (sum of Forces) = mass x acceleration.

      The force balance equation in cycling could be seen (very approximately) as F_human – F_drag = mass x acceleration.


      In cycling, most power meters measures force between human and crank arm (or chain, pedal, etc…), i.e they measure F_human directly. That, times the angular velocity of the crank arm, gives a clean calculation of external power output.

      Now, there are some power meters that try to estimate cycling power by calculating all the other terms in the equation to estimate F_human, using GPS & wind estimates for drag. Needless to say, they are going to be less accurate.

      Now, keep in mind these methods are estimating Power Output. Power Input is essentially how much energy is the body using to generate that Power Output. Gross Mechanical Efficiency can be defined as:

      Efficiency = Power Output / Power Input x 100%. In cycling, its around say 20-23% in most cyclists. This efficiency is a key element to improving performance, so it is very useful to measure both power output and power input (i.e. anaerobic + aerobic energy pathways through heart rate, VO2 consumption, etc…)

      Running: Like a pseudo cycling power meter measuring wind resistance & GPS, Stryd is estimating all the other terms in the force balance equation. So there is going to be some error right off the bat. Ideally, the equivalent to a strain gauge cycling power meter would be shoes with load cells measuring force during running (this will measure F_human directly)

      But there is a bigger, fundamental issue with measuring power in running, even if you measure F_human directly. What is a true power output?

      If you are running on flat land, the horizontal component of the reaction force will average 0 over the course of a full stride, so the net power would be 0.

      You could measure just the propulsive phase force. You could also measure the vertical force accelerating the body upwards (before gravity brings it back down). But both of these could yield power numbers that get larger as the runner converts to a style that is actually less efficient, so that doesn’t make much sense.

      Whatever power estimate you derive from a biomechanical model of the body must also work for hilly terrain where power estimation due to change in vertical potential energy actually can be estimated.

      So there are a lot of problems with measuring Power Output in running.

      Now Stryd has admitted they aren’t measuring Power Output in running, but Power Input. That means they are essentially estimating energy expenditure (anaerobic + aerobic). Heart rate can only give a proxy for aerobic, so when you sprint up a hill suddenly, there are anaerobic contributions that perhaps they can give an okay estimate of with some statistical modeling of F_human.

      But you can’t estimate running efficiency because you are only measuring power input.

      So, I applaud them for creating a novel product, but it is far away from the running equivalent of a cycling power meter.

  89. Andrea

    Hi Ray,
    when do you plan to release the Stryd Pioneer’s reviews?
    I’m thinking about a Christmas present ….. for me!

    Thank you for the great work.

  90. Andrew

    Running with power is a very interesting concept. I understand since this is new territory it may take a while before you can complete an in depth review. However in that case would you be able to do another “First Impression” with the new chest strap version of stryd (stryd pioneer I believe it’s called)?

    For me I think the largest items that prevents me from simply taking the plunge are:
    1) I have a Forerunner 620. What are the tradeoffs of using stryd (given power isn’t natively supported)? Would I simply lose the cadence value from the 620’s own accelerometer and Garmin running dynamics? (Or perhaps just the former if I wear HRM-Run & stryd?)
    a) On a side note I’m not against wearing a HRM chest strap. Though wearing two for every run seems a bit excessive.
    2) A review or first impression from you on the production version given that there have been some changes since this “first impression”

  91. Javier

    Hey Ray,
    Would you use the waterproof test chamber to check if it would survive a half or full iron swim stage? (They claim IP67…1mtr/30mins)

    • Ironically, my chamber doesn’t go that low! I believe the min is 5m, since basically everything below that I could test by just tossing it into a pool (or even a bathtub).

      Still, I’ll toss the Stryd strap into a tub or something for a number of hours to validate it, but I don’t expect it to be an issue. The pressures at 1m are pretty low for these types of designs.

    • Javier

      Appreciated! :-)

  92. Andrew S

    Sounds like Suunto recently added Stryd as a full on feature. Great for them. Hopefully this nudges Garmin to do the same. Any word on when IQ is supposed to open .fit files to 3rd party apps? Right now Stryd’s app is OK in the sense that it can convert cycling speed to pace, but its only instantaneous pace (useless as far as i’m concerned) and i’m not totally ready to train by power and not by pace. Also skews all my 920xt Cycling Data! Minor, I know…but still!

    • When I checked in last week, it was still on target for release this quarter.

    • Hey, Ray.
      Where can I find the updates on Garmin integration you’ve mentioned?

    • Unfortunately Garmin has pushed it (.FIT file 3rd party data recording) now till ‘Summer 2016’. :(

    • Kris

      Would the delay by Garmin be due to competition? I’ve run with Garmin Running Metrics quite a bit and other than report the data as a calculated ‘power’ value, Garmin seem to have all the necessary hardware and data to create their own ‘Garmin Power’ metric with a firmware upgrade should the demand be there.

      Do others agree??

    • No more delay now. Stryd announced a beta program to users about a week or two ago (via e-mail to registered customers), and Garmin also announced a beta program. I think the go-live date for production is July 17th.

    • Wizbang

      July 18 – any updates on the Garmin beta program for power metric while in run mode?
      How would we go about getting on the beta program?

    • If you were a Stryd customer at the time, you can dig around your e-mail for instructions on joining the beta program. Else, my guess is if you sent a note to support they could help out.

    • Hi Ray. Do I need to have a Stryd device to participate in beta program? Or HRM-Run metrics are enough? Thank you.

    • Yes, you would.

      It’s a Stryd beta program that leverages their device to gather data metrics.

  93. Kailangel

    I’m a Suunto-sponsored ultra trail runner and really looking forward to this product. Just one question I had where I haven’t figured out a conclusive answer yet. A key thing for me is efficiency in running with running poles, uphill, downhill and flats. Any insights?

    If you need a trail-ultra test user that does a lot of stuff in rough terrain with lots of vertical and often uses poles, hit me up :)

    • Sebastien Spieser

      At first the firmware did not allowed power readings while walking; now its fixed, but since then I’m injured so never had a chance to try:
      – power values while walking steep hill
      – power values while walking + pushing hard on the poles – trying to have the same vertical speed ascent !
      If you are abble to give a try, let m know ;-)
      I’ll test this in a few weeks…

  94. Hello there.
    Looks like Stryd is already selling their device – link to store.stryd.com
    Can’t find anything about Garmin integration on the Internet. Any updates?
    Workaround “train in bike mode” does not look that good…
    Thanks in advance.

  95. Aaron

    Wanted to put this out there to your Stryd users. We (at SportTracks) are seeing more Stryd data come in, and one problem seems to be the cadence number is doubled. What are others experiencing? Is this specific to certain watches, models, or firmwares?

    We’d like to give our customers some guidance on this, and hopefully not make a hack specific to Stryd data to fix the cadence doubling bug.

    • Marathon Man

      I’ve also reported this directly to Stryd. I’m sure they will be here shortly to provide comment.

    • Full disclosure: I’m on the Stryd team.

      Very happy to know that your platform supports Stryd!

      The cadence doubling problem has the following cause. Some watches (focused on cycling) expect cadence to be reported in revolutions per minute (90 would be common). Others (focused on running) expect steps per minute (180 would be common). A somewhat inelegant solution that would probably work in practice would be to detect when the cadence is unreasonably high and half it. If we identify better solutions, we will tell you.

    • Hey Robert,
      Could you please answer my question above (regarding Garmin integration).
      Thank you.

  96. J H

    As it was a luxury purchase I’m selling my stryd in the UK:

    link to ebay.co.uk


  97. EB

    This post is now 15 months old. And now lots of people have them in their hands. Not only have I searched the Stryd website, but I’ve read all the posts below and had a look in the scientific literature.

    I was sceptical, but they don’t make as silly claims as the BSX insights lot, so I thought I’d give them the opportunity to demonstrate this worked and not say anything.

    I think it is now the time to say the evidence to back up the use of this device is almost non-existent. There are also obvious logical flaws, for example sensing energy loss variation related to changes in terrain or wind strength/direction.

    This seems much more likely about kerching than anything useful. I can see why the gullible and the greedy have got on board.

    Incidentally, the graph above shows force and doesn’t specify direction of the force. To turn a force, even if we assume they are getting the exact right type of force, also needs to be combined with distance to calculate power….

    • So, to recap:

      A) You’ve read a lot on the internet, but haven’t actually tried it.
      B) Despite all that reading, you didn’t read the part about understanding elevation due to barometric altimeter inside?
      C) You mention BSX being troubling, yet they more than Stryd actually do have scientific studies (one was published back in December by a non-affiliated entity) showing accuracy.

      Which isn’t to say Styrd is perfect. Wind is a huge issue, and one I believe they under-estimate the issue with. But to say it’s useless and purchasers are guillable is a pretty big stretch.

    • Chris O'Shannassy

      I’m a Stryd user and I love mine. There’s definite issues with wind playing havoc on the barometer and hence messing up the power numbers. It fails to account for really soft surfaces such as sand. There’s some lesser issues too – it doesn’t account for the braking effort you put in on very steep downhills and it underestimates power when walking up very steep hills. But I’ve had mine from the start and now when I run it’s almost always against power and duration, regardless of the terrain I’m running on. I’d not want to have to go back to running just based on some mix of HR/Pace/Cadence like I was previously. The Stryd has been great.

    • EB

      Ray, you suggest I should try it. That would be a single anecdote and be subject to subjective bias. I’m actually disappointed you think such a small sample should sway an opinion. If I had something and my subjective opinion was negative, but then good research came out that was positive I would have to change my mind.

      And I don’t mention the word ‘elevation’. I knew it had a barometric altimeter. Where did you get that from? Are you suggesting that it has multiple barometers and senses wind using the Venturi effect or something?

      I also said it was ‘more’ about kerching than anything useful. Eg relative not an absolute term as you suggest. Similarly I didn’t say purchasers are gullible, I said I can see why the gullible have got ‘on board’. Not only did I not use the word ‘purchaser’, but even if you imagine ‘on board’ only relates to purchasers I didn’t say the gullible was the only group of purchaser. Please don’t put words in my mouth.

      You mention, above, that you had nothing to compare the numbers to as it was a brand new type of device. This is not your responsibility. It is their responsibility to publish the evidence, so anyone can scrutinise it. Anyone with whatever expertise they have. They have chosen to use the word ‘power’, which is a word that actually means something already – they need to justify their use of a real word that is already well defined. It would be very different if they had chosen to invent their own unit, eg. ‘Stryd Factor’, but they didn’t.

      I’ve read the BSX research before and found it to be entirely unconvincing, particularly as justification for the dramatic claims made on their website. The impression I has was of people trying to blind people with (pseudo) science in a similar way to alternative medicine/woo has. However, I will recheck to see if any new research suggests I should change my mind.

    • EB

      Hi Chris,

      I didn’t actually say it was useless or that you were gullible. I don’t know where Ray got that from. In fact I think it quite possible the opposite is true.

      I believe it is entirely possible, possibly even likely, that the number it gives can be used to improve training, as you anecdotally have found. My objection was to the use of the word ‘Power’ which is a well defined word that even has an SI unit (Watt). A Watt is 1Joule per second. Power can be calculated by dividing work done by the time taken to do it. I just don’t think that number should be called ‘power’.

      As regards gullibility, I do believe some of the people who have ‘got on board’ are gullible, but I never said that all purchasers were gullible. Reading your post; I think you probably decided to complete the purchase whilst maintaining a healthy dose of skepticism.

    • EB

      Ray, if this study, from the 15th if December, is the one to which you refer (“Wearable lactate threshold predicting device is valid and reliable in runners” J of Strength and conditioning research”) I hope you are basing your assessment on having read the full paper and not the abstract – there is no where near enough in the abstract to assess it. It does however say the experiment was in ‘runners’. The gastrocnemius muscle (superficial calf) simultaneously both bends the knee and plantar flexes the ankle; not an obviously good choice in cyclists is it?

    • EB – Your exact words were – “gullible and the greedy have got on board.” Try and re-mince it however you’d like, but those be your words. I need not put them in your mouth, you’ve already done so.

      As for “you suggest I should try it. That would be a single anecdote and be subject to subjective bias.”

      No, it’d be understanding how it works more than just reading about it.

      Of related note, yes, I’ve actually read the full BSX study. It doesn’t sound like you have though.

    • And to be clear, I’m far from pro-Styrd. Anyone who follows what I’ve written or said in podcasts over the last few months will realize that. I’ve often talked about challenges with wind and certain ground types (i.e. sand).

      At the same time, I also thing posts like yours appear to be little more than stirring the pot for the sake of stirring the pot. Without supplying any actual usage data to back up claims.

    • Chris

      Hi Ray,

      Are you going to post an indepth Stryd review in the near future? I am debating on buying one and would like to hear from a trusted source before I commit (or hold off.) Also, hypothetically, is running power a possible metric that the HRM Run strap V2 could report?



    • Joel

      I can agree with EB in the sense that power is a well defined unit and one that maybe shouldn’t be use in this case. In the case of bikes, as far as i understand, you are measuring the actual power produced at certain areas of the drivetrain. As an engineer, that makes sense to me. Now, I’m not sure what the running “power” meter actually uses to measure “power”, but i think the HR, speed and time should be enough to calculate. But all this would be assuming that the HR is well understood, and sadly is not. Everybody has a different HR threshold while training. I like 145 on E (8:10 mpm) runs, but i can go as high as 190s (mid 5s) on short races with hills. There are some people who train on 140s @ 7:20 mpm, but can’t touch 180 on hard workouts. Sadly there I dont think there is an easy way to calculate the power produce when running. The heart is the body engine but is not even close to be the same on all people. You can call is Chimichanga as far as i care. Is it useful? Sure…i can see how putting a new metric with using HRM, pace, time, elevation, and other variables can be helpful to track progress.

  98. Andrzej

    Hey Ray, do you think Garmin will ever allow power channel on “Running” activities?
    Having a Stryd and using it in everyday workouts is the only reason not to jump ship from the current watch that is 100% Stryd compatible, but lacks in other capabilities.

    • I’m sure at some point. Failing that, once they allow Connect IQ to write .FIT files with extended data (pushed back to this summer), then it becomes a semi-moot point.

  99. James

    What are the chances that Garmin will produce a GPS-watch with a strap with embedded power functionality? That must be the best way in terms of competition.

  100. Paul frost

    Like others I’m puzzled why you haven’t done any more testing, as the product has been around a while now. Your initial feeling seemed to be it may have some value on hilly/rough terrain, which is primarily where I run.

    • Singular reason: It’s a pain in the butt for those using Garmin devices to use. Thus, when I go for for a run each day, it’s yet one more thing to deal with pre-run/during run/post-run, that interrupts the normal workflow.

      I have to use it in cycling mode, which means I don’t get fields like lap pace. Nor can I use features like the metronome. Next, when it comes to uploading, I have to go back and change the activity type in three places (Garmin Connect, Strava, Training Peaks). Plus, I then don’t get running cadence recorded either.

      This all works of course on Suunto, but not Garmin.

      Now none of this is directly their fault. It’s largely Garmin failing to deliver on their promises of opening up Connect IQ to better handle this (now slated for summer). But as with any business, if you depend on another company for your own business, then you’re at their mercy. In this case, those items above are a big enough blocker for me that once I’m done getting everything else dealt with – it’s just one more pile of things to sort through.

    • Thanks for the quick response. I’m a Garmin user (920xt) so those issues would be a block for me too. Pity, as Huub are giving a Stryde away with a £400 wetsuit and it would have been a good incentive to get the better suit.

    • Chet

      Has the most recent version of the STRYD Running With Power Connect IQ App for the Fenix 3 resolved these issues?

  101. Paulo Sousa

    Ray, do you know if Stryd is going to release a different version without being on a HR strap?

    Best regards

    • I had the same question in mind. I find it weird that the prototype was this clippable device and the release version is just another gadget strapped on my chest !
      Also, are the power meters as foot pod more accurate? As a mountain runner I would tend to think that they would be able to be more accurate and take into account the change of terrain (technical terrain…)
      My understanding is that we are at the very beginning of the running power meters and more should come our way soon


    • panos

      Your understanding is correct, we are at the very beginning of running power meters.

      There is another thing that you have to understand, which is that at the same moment we are at the END of running power meters.
      The reason for that is that running with power, has at best, the same value as running with pace whatever the terrain.

      The claim that runners can now have the same benefits as cyclists using a power meter is a huge lie, to say the least.
      I am using a cycling power meter for one year, i see what i am doing with, how it helps me and what more i could do with it if i had the time/money/interest to take advantage of its full capabilities.
      I am primarily an ultra trail runner and initially interested in stryd (which is basically an app that estimates power) and rpm2 (which actually measures running power) and no matter how much i strive, i can not find how a running power meter could be more useful than running pace or how could i do the same things with a running power meter as i can with a cycling power meter.

      Maybe ray could do the running crowd a favor, by putting out a list, like cycling power meter VS running power meter, what you can do with a cycling power meter and how do it relate to a running power meter.

    • Ze

      For flat running, you are right that speed is essentially the running version of power, and it is mostly all you would need (as long as value is accurate within a few seconds for sprints).

      Really you would want something that knew your instantaneous speed and your bodyweight to get a better correlation to how much work you are doing on that day. (If you lose 5 lbs of water weight, you aren’t generated as much power at the same speeds as before the weight loss).

      If you had an ideal power meter, you wouldn’t have to input bodyweight because the device would be able to measure the forces at the feet directly. That is a true measurement, although it doesn’t convert to a “power” metric directly.

      For training on anything other than flat, it gets much more complicated.

      Stryd is not measuring force, they are measuring kinematics on the torso and making associations to work effort based on that.

      What is worrisome (based on reading their feedback in the Stryd forum) is that they are making assumptions about what the best running style is in how they calculate power. This is absolutely arse-backwards! The ratio of power out (i.e. speedxweight on flat) divided by power in (energy consumption) should tell you if a running style is efficient or not.

    • Very good insight from both of you.
      I am still discovering power meters as I have never even used one for cycling. Like I said, as a mountain runner, I dont have such tools to help my training. So far, I’ve used heart rate and NGP (Normalized Grade Pace) as tools.
      I am not surprised that the Stryd power meter has to do such assumtpions as it is located on the torso.
      Would a power meter located on the shoes fix such an issue ?

      Panos, your insight is really interesting, we could be at the end of it as well. As I am reading “Run with power” (Jim Vance), I was convinced that it would be a revolution. probably I got carried away ?
      I am still awaiting to see future products and would love to see Ray make a good review of the final version of the Stryd.
      Even if the running power meters dont take off, I am still looking forward for better tools for training.

    • Ze

      A “power meter” in the shoe (i.e. something that measures forces between feet and ground) could be better. However, a sensor package in the shoe that is measuring just kinematics is likely to perform much worse than on the torso.

  102. Robert Monaco

    But, how is this little clip on the back of your shorts measuring power? Wouldn’t there need to be some kind of force plate in your sneaker?

  103. Mike C

    I was listening to Podcast (and I believe it is in the book Run with Power) that discusses this. Unlike cycling where watt/kg is very important, it appears that speed/watt may be more important in running. An improvement in speed/watt may show that you are becoming more efficient at running and can run at the given speed using less work.
    I am interested in seeing in the Running Power Meters can perform but holding off on pulling the trigger on getting one until it is more supported on my Garmin watch.

    • Notofru

      Well then, good news! There is the Stryd app that I personally don’t like very much, but there is also the IQ data field that gives you your power numbers while you run and afterwards in Garmin Connect.
      Unfortunately this is only 3 or 5s rolling average of power, you don’t get lap power or average power.

    • Mike C

      That is good. Is it just a datafield though or can you program workouts into Garmin Connect based off Power yet? (e.g. when you go above or below the predefined range for the interval you get an alert)

    • Notofru

      Nope, just the data. Power is not supported by Garmin in any way – yet.
      Some people are of the opinion that this is because they want to introduce their own power meter in the future.

  104. A.J. Mesalic

    Ahhhh you’re on my home track (UNLV). Look me up. I’ll show you some proper hills around here! You found the only flat spot in the area. haha. Lots of fun endurance sports opportunities nearby.

  105. richard braginton

    Hi do you think this will work on the bike ? have you any plans to test it whilst cycling. Do you think the power meter manufacturers are getting twitchy