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{{DISPLAYTITLE:Stryd footpod review (Dec 2019)}}
Stryd is one of the most useful and impressive running technologies available. It's a [[Footpod]] that analyzes the movement of your foot with greater accuracy than most traditional Footpods, and with vastly greater accuracy than GPS. While a lot of the Stryd marketing focuses on their "running power meter" functionality, I see the greatest value coming from their accurate measurement of pace and distance. If you look at my [[GPS Accuracy| testing of GPS Accuracy]], you will see that Stryd gives a far more accurate measurement of distance than any GPS watch. It accurate enough that it really doesn't need any calibration, and unlike GPS, it should work in any situation (see below for details.) Not only is it providing accurate distance measurement, but it provides real-time pace, something that's impractical to achieve with any GPS device. While I believe [[Running Power Meters]] are quite different to cycling power meters and are more of a "power estimate" than a meter, I think that Stryd's power estimate has improved to the point where it's a valuable training and racing tool. At $220 I think that Stryd is good value for money, and it's one of the few running devices that I would replace unhesitatingly if I lost it.
{{BuyStryd}}
* '''Form Power, Ground Contact Time, Vertical Oscillation, Leg Stiffness'''. These fields are all available via the Garmin [[Connect IQ]] data field, and can be viewed using Garman Connect.
[[File:StrydGarminConnect.png|center|thumb|500px|A view of the data collected using the Garmin [[Connect IQ]] data field with Stryd also connected as the Footpod, using a [[Garmin Fenix 3]].]]
=Stryd and Running Economy=
One advantage of Stryd is that it's power estimate can be used to then estimate [[Running Economy]] and [[Heart Rate Drift]]. You can read more about this at [[HrPwr]].
=Testing Distance and Pace=
I tested the distant accuracy of the Stryd using the same basic methodology as I do for my [[GPS Accuracy]] testing. (See [[GPS Testing Methodology]] for details.) I used a [[Polar M400]] configured to use the distance from the Stryd footpod. As you can see from the results, the Stryd is remarkably accurate, far better than any GPS device I've tested. My testing of pace is more anecdotal, but I've been able to hit my target paces using guidance from my Stryd. I've tested using a range of paces from 10:00 min/mile to 6:30 min/mile and the Stryd allows me to cover a given distance in just the right time.
Stryd seems reasonably responsive to changes in pace, though it's hard to determine how the smoothing of Stryd interacts with any smoothing of the watch. I've found Stryd responds within a few seconds, though the power estimate is a little slower to adjust. Recent firmware updates have improved the responsiveness of the power estimate, though it's still a little slower than I'd like on rapidly changing slopes.
=Treadmill Problems=
The Stryd is so accurate outdoors, I couldn't understand why it was so bad on a treadmill. To my chagrin, I discovered that the Stryd Footpod was right, and main problem is my treadmill was speed display is way wrong. Accurately calibrating a treadmill proves to be rather more complex than I'd have expected, as the treadmill will slow down when your foot is in contact with the belt, then speed up when you're in the air. For details on how to evaluate your treadmill have a read of [[Treadmill Calibration]].However, this variation makes it tricky to know what the "true" speed should be. Obviously, the average speed of the belt is completely wrong, as the speed of the belt while your airborne has nothing to do with your running speed. During the time your foot is in contact with the belt, should you use the minimum speed, the average speed or the maximum speed? With my treadmill, the difference between minimum and maximum during contact is about 15%, and between average and minimum is about 9%. I've found Stryd seems to be quite close to the minimum speed rather than the average during contact. I calibrated my treadmill and then calibrated Stryd to the corrected treadmill speed, which is a lot of effort and tricky to get right. A much simpler solution is to use the [[North Pole Engineering Runn Treadmill Sensor]], which measures the treadmill speed with far less effort and greater accuracy. [[File:Treadmill During Contact.jpg|center|thumb|300px|Treadmill speed during contact with the belt.]]
=Testing Battery Life=
I've not done a single long run that would allow me to test the battery life for an ultramarathon. However, on multiple shorter runs (25-120 minutes) I found that Stryd was reporting 10% battery life left after 5.5 hours, which is far short of the claimed 20 hours' battery life. However, this may well be due to one of the many watches I have paired to Stryd keeping the pod alive well after the run, plus I tend to pair my Stryd to different watches many, many times. I will attempt some more realistic testing in the near future. I've seen one report of an ultrarunner who completed 100-miler in 28 hours and had 27% battery life. This is anecdotal, but encouraging.
=Stryd and Critical Power=
The Stryd app has started to support [[Critical Power]], a concept more widely used in cycling. The Stryd method of calculating Critical Power is to use one of 5Km/10Km race time, or a test protocol using just two durations. The research I've found on Critical Power suggests that more data points are needed to provide a valid measure of Critical Power, and especially W' (anaerobic work capacity). Most research uses a fixed power output to exhaustion rather than a time trial. A time trial includes aspects of pacing and skill, so this seems a poor substitute. (Typically, CP tests define "exhaustion" as when cycling cadence drops below 50 RMP.) I'd recommend using more test runs and using one of the many Critical Power calculators available online. Stryd also has an [https://blog.stryd.com/2019/07/09/introducing-auto-calculated-critical-power/ automatically calculated Critical Power], but I've not seen any independent validation.
=Stryd's Power Estimate Compared with Cycling Power=
I performed an incremental test with both Stryd for running and my Tacx Neo 2 for cycling. For running, I used a 400m track, increasing my pace from 10:00 min/mile to 5:30 min/mile over 14 laps. I then performed a similar test cycling, increasing the power gradually. I then mapped the power from each to my heart rate. In both cases I found a reasonable linear relationship between power and heart rate. Using the linear relationship, I found that Stryd power is generally quite a bit higher than Cycling power. For me, Stryd Power = (Cycling Power + 40) / 1.13, so 100w in Stryd is about 70w Cycling.
=Using Stryd With Your Watch=
Here's my notes on the compatibility testing I've done so far. I've had occasional issues with devices connecting to Stryd at the beginning of a run. I've not found any pattern to this, and it seems to impact both Bluetooth and Ant+ devices, so make sure you have a connection before starting your run. I've also occasionally forgotten to turn off auto-calibrate, which is another gotcha.
