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{{DISPLAYTITLE:Stryd footpod review}}
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. 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. 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 if you understand their limitations they can still be usefulStryd's power estimate has improved to the point where it's a valuable training and racing tool. At $200 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. (Note that you need to have access to an iOS or Android device to setup Stryd.)
{{BuyStryd}}
=The Metrics=
* '''Pace and Distance'''. My testing has shown that the Stryd is stunningly accurate in its measurement of distance. It's the only [[Footpod]] that is accurate enough that it doesn't require calibration, something that greatly improves its usability. If you look at [[GPS Accuracy| my testing of distance accuracy]] you'll see that the Stryd is right at the top of the chart, and is far more accurate than any GPS device I've tested. This accuracy is also reflected in its measurement of current running pace. I think that this feature alone makes the Stryd good value for money. (Stryd doesn't use or provide GPS data, it uses accelerometers. Depending on the watch, the data from Stryd can be combined with the Watch's GPS data so that Stryd gives distance and pace, and the watch's GPS can be used for navigation.)
* '''Elevation. '''I suspect that Stryd is providing remarkably accurate elevation information. Due to limitations on data export I've not been able to perform any statistical evaluation, but anecdotally the data looks really good. Obviously, the Stryd cannot provide any absolute altitude information, but it does seem to be able to measure relative changes far better than either GPS or barometric altimeter's. At the moment, this information is not as directly usable as I'd like, as it's only available in real time via their, not their watch integration. If you use the Connect IQ data field, it will record elevation as a custom data track, and it is possible to copy this to the standard elevation track using plugins to Sport Tracks.
* '''Running Power'''. As I talk about in my page on [[Running Power Meters]], I believe that they are a flawed concept, but if you understand the limitations they can still be usefulnot power meters at all. SoLike other running power meters, Stryd it does not actually measure running power, but attempts to estimate what the power would be based on the things it can measure. My assumption is that it is mostly using pace and elevation change, possibly along with [[Cadence]] or Ground Contact Time. As discussed in the section below on the testing running power, I have found that the latest Stryd seems to give firmware gives a reasonable good estimate of relative intensity for flat and uphill running, but seems to underestimate relative intensity on the downhill sections. I've found that with some testing to understand the limitations, I've been able to use Stryd to more effectively pace myself on hilly runs. My approach is to keep my Stryd power estimate constant between level ground and uphill sections, which means I'm much slower going uphill. If Stryd gave a better power estimate downhill I could use it for downhill pacing, and hopefully they'll improve their estimate soonas well as giving additional insight into [[High Intensity Interval Training]].
* '''Form Power.''' Stryd describing this metric as the "running in place power", but it's unclear what that really means more if it has any value. They suggest that a decrease in this value represents improved [[Running Economy]], but there is nothing to back that up.
* '''Cadence'''. Cadence is fairly trivial to measure for even a far simpler [[Footpod]], so Stryd nails this easily. It's arguably one of the most important running metrics, so you should pay attention to this. There are far cheaper ways of measuring cadence (like [[MilestonePod]]) but it's nice to have this included in the Stryd.
File:Stryd Comparison (2).jpg|Looking sideways you can see the Stryd and Garmin Footpods have similar openings for shoe laces.
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=Testing Running Power=
It's important to realize that Stryd is not a [[Running Power Meters| Power Meter]] in the way that cyclists have power meters. Stryd does not measure power in direct, absolute terms, but creates a mathematical estimation based on running pace and incline (and possibly other factors.) This means that you can't easily use Stryd to evaluate improvements in running form or [[Running Economy]], though looking at the power estimate against heart rate might give some interesting insights. However, I've found Stryd's power estimate to be quite useful in the real world. It allows for far more accurate pacing over undulating terrain than pace or heart rate. It can be a bit of a shock to see just how slow you have to go uphill to maintain an even effort! Earlier versions of the Stryd firmware tended to dramatically underestimate the effort of running downhill, but as of 1.1.2, the estimate seems far better. The graphs below are showing my runs up and down a local hill. It's not a very long Hill, but it is fairly steep, averaging 6% with sections nearer 10%. In these tests, I'm aiming to keep an even effort based on the Stryd power estimate. You can see that not only is the Stryd power estimate reasonably stable, but so is my heart rate, indicating that the Stryd estimate is doing a remarkably good job across dramatically different inclines. Though this is still a modeled, estimated power intensity, it's far better than anything else available to us and is good enough for real world usage. If you need to accurately pace yourself on undulating terrain (Boston marathon anyone?) Then I'd heartily recommend using Stryd. Of course, you'll need to work out what your estimated power level should be in order to match your target race time, and this is something you'll have to do by trial and error. Simply run a course of the mirrors the race terrain and compare your average pace to your target pace. If you're too slow then your power target will need to be a little higher, and vice versa.
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File:StrydEvenEffort (2).jpg|Here my HR is a little higher on the downhill than the power would suggest. This might be partly due to running form or warmup.
File:StrydEvenEffort (3).jpg|Across these two repeats you can see heart rate and power estimate match really closely.
File:StrydEvenEffort (4).jpg|Another almost perfect match.
File:StrydEvenEffort (5).jpg|My heart rate is slightly higher at the top of the hill, but matches fairly closely.
File:StrydEvenEffort (1).jpg|A little bit of variation, this time with heart rate lower than power on the downhill.
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Another use of Stryd is in interval training. For most traditional intervals, where you're performing them on the flat (e.g. a track) then using pace is probably best. However, for Hill training, Stryd will give you a much better idea of your intensity than pace or heart rate. The graph below shows me running hard up the hill, then resting on the way back down. You can see that both my heart rate and power estimate rise on the uphill and decline on the downhill. You'll notice that my heart rate response is rather slower to the change than the power estimate, making it more useful for providing a useful, real-time estimate of intensity.
[[File:StrydHardUpEasyDown.jpg|center|thumb|400px|Traditional Hill training, focusing on high intensity on the way up and easy back down. Power data from Stryd, Heart Rate from [[Wahoo TICKR Run]], elevation/distance/pace from GPS using [[Suunto Spartan Ultra]].]]
I've found Stryd to be particularly useful in [[High Intensity Interval Training]], especially when using the [[Polar V800]] that has a native power support. With the V800, I can set the watch to display the maximum power for the current lap, which gives me a far better idea of how hard I'm pushing it on each interval than is possible any other way. You can see in the graph below that in short HIIT intervals the heart rate is a lagging behind power estimate, and my heart rate is still rising after I've slowed up.
[[File:StrydHIIT.jpg|center|thumb|400px|A HIIT interval from my [[Katana Run]] workout.]]
==Stryd Power Estimate or Heart Rate?==
The use of heart rate for training has been established for many years, and heart rate based training has some useful advantages, as well as some significant shortcomings. I think the Stryd estimate of power output overcome some, but not all of the issues with heart rate based training. Personally, I don't see this type of power estimate completely replacing heart rate based training, only augmenting it.
* Heart rate responds to exercise intensity with a delay, while Stryd's power estimate is much closer to real-time.
* During longer exercise, [[Heart Rate Drift]] occurs that generally causes a higher heart rate for a given intensity. The reasons for this drift are complex, and include dehydration, fatigue, carbohydrate depletion. Using Stryd's power estimate ignores this drift, though it's unclear to me when to use heart rate and when to use the power estimate. In some situations, it seems likely that the drifted heart rate is a better estimate of intensity than an unmodified power estimate.
* There is a widespread myth that [[Maximum Heart Rate]] can be calculated, leading to some erroneous assumptions of how a given heart rate relates to the percentage of exercise capacity. In practice, both Heart Rate and maximum estimated power require a practical test.
* A common use of heart rate data is to allow an athlete to train at their [[Lactate Threshold]], often referred to as [[Tempo Runs]]. The belief is that this training intensity is especially beneficial, though the available science indicates the opposite. If Tempo Runs made sense, then Stryd's power estimate would be quite valuable for hitting that pace accurately. I'm sure that many runners will use Stryd this way, even though the science indicates it is ineffective.
=Watch Support=
Stryd has support for a remarkable number of running watches. It supports both Bluetooth and Ant+, and it can look like a standard Footpod, a cycling power meter, or provide more sophisticated data. There are a large number of combinations of watches and configurations to consider, so I'll look at the general integration approaches and then look at specific watches.
=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 my treadmill was 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]].
=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.