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From Fellrnr.com, Running tips
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{{DISPLAYTITLE:Stryd footpod Running Power review}}Stryd is one of the most useful and impressive running technologies available, with four key benefits. It* '''Accurate Pace'''s . Stryd is 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 vastly greater accuracy than GPS Accuracy]], you will see that Stryd gives a far more accurate measurement of providing much better pace and distance than any GPS watchdata. It 's 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 Because of it providing accurate distance measurement's accuracy, but it provides can provide real-time pace, something that's impractical to achieve with any GPS deviceas GPS requires quite a bit of smoothing, giving only a recent average pace. * '''Running Power'''. While I believe a [[Running Power Meters]] are quite different to cycling power meters and are more of a "power estimate" than a true meter, I think that Stryd's power estimate has improved to the point where it's a valuable training and racing tool. Unless you run on perfectly flat ground, running power is a better measure of effort than pace. * '''Fitness Measure'''. I use the relationship between Stryd's power and my heart rate to evaluate my fitness over time, as well as my fatigue during a run. This [[HrPwr]] has been more useful to me than any other metric as it can be calculated in real time. * '''Running Form. '''Stryd is the first device I've found that provides data on your running form that is actionable. While other devices can provide a lot more data, it's typically hard to work out what the data means. Stryd allows you to compare your running form with other runners, which can show areas for improvement. Both the Footpath Visualization and the Stryder Distribution can give meaningful and usable insight into your running form. Hopefully, Stryd will continue to improve this data, allowing you to compare your footpath and distribution with runners based on their fitness (crucial power.) 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}}
=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. (It's possible to tweak the accuracy with calibration, but out of the box is should be much better than GPS.) 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 altimeters. 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 not power meters at all. Like other running power meters, Stryd 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 firmware gives a good estimate of relative intensity. I've been able to use Stryd to more effectively better pace myself on hilly runs, as well as giving additional insight into [[High Intensity Interval Training]]. The current version of Stryd has "wind detection" to adjust the power estimate based on ambient wind.
* '''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.
* '''Ground Contact Time'''. Ground Contact Time is how long each foot spends on the ground,'' ''and it's frequently often suggested that a lower value represents a better Running Economy though the research is mixed.* '''Vertical Oscillation'''. Because Stryd is a Footpod, it has no way of measuring [[Vertical Oscillation]]. Therefore, Stryd is estimating vertical oscillation from things like Cadence and Ground Contact Time. My testing indicates shows that Stryd is underestimating gives a lower vertical oscillation compared with other devices. However, This is most likely because Stryd suggests that this is because they are measuring estimating the vertical movement of the runners' center of gravity rather than just the torso, which is a more appropriate and useful measure. Look for Fredrik Zilléns' excellent video "[https://youtu.be/pvt0lzvXTxc?si=5kHFHFWpp2t1Au_K Up/down movement when running is not what it looks like]" for more details.
* '''Leg Stiffness'''. It's possible to model a runner with their legs representing a spring and the rest of the body as a mass. When a runner lands, they decelerate their bodies vertical movement and the rate of deceleration can be used to estimate the stiffness of the "spring". The stiffness of this hypothetical spring is related to Cadence, with a higher cadence having a stiffer spring. The preponderance of evidence suggests that a stiffer leg stiffness is more efficient, and that fatigue tends to soften the stiffness. There are various ways of estimating leg stiffness, such as measuring the vertical ground reaction force and vertical movement. This gives the force applied and the amount of deformation of the "spring", resulting in a reasonable estimation of stiffness. Another approach is to use ground contact time and cadence, which is how I suspect Stryd is estimating stiffness. Personally, I suspect that this is an overly simplistic model.
Note that Stryd provides no information on foot strike parameters such as pronation, or foot landing position.
File:Stryd Wind (2).jpg| Here's the Stryd pod on the shoe.
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=Footpath Visualization=
The latest versions of Stryd support "Footpath Visualization", which shows how your foot moves during the running cycle. Two Stryd pods gives you both feet, but the latest version supports this visualization with just one pod (obviously showing only one foot.) You can show your footpath for a specific run, but I find the ability to show your average footpath for a month at a given pace to be the most useful. Below you can see the comparison between October as a solid line and September as a dashed line (blue is right foot). This is my footpath for running between 3:53-4:02/Km, and you can see my right foot is going higher than my left.
[[File:Footpath Visualization.jpg|center|thumb|400px|Stryder Distribution]]
Things become more dramatic when viewed from the rear, where you can see my left foot is going a lot wider than my right foot, and the problem has become worse. This is something I can work on, looking for flexibility and strength asymmetry.
[[File:Footpath Visualization Rear.jpg|center|thumb|400px|Stryder Distribution]]
The main thing that's missing is the ability to compare your footpath to other runners. If you could show how your footpath looks compared to the much fitter runners when your pace is similar, you would probably see areas for improvement.
=Stryder Distribution=
I find the "Stryder Distribution" graphs to be a useful way of evaluating how my running form compares to other runners. It shows where you are on a distribution curve against runners of different age categories, and more importantly, at specific paces. Below is the graph comparing me to all age ranges while running at 3:25-3:35/km pace. You can see my [[Cadence]] is higher than average, probably because my stride length is limited and I'm having to use a faster cadence to reach that pace. My duty factor, which is the percentage of time in contact with the ground, is lower than average which is good, but might be due to my high cadence. My Vertical Oscillation (VO) is quite low, which shows my leg swing and bounce are both good. Leg Spring Stiffness is average, so there's room for improvement with strengthening my leg muscles. Impact Loading Rate is a little lower, showing I'm not jarring on landing. So, you can see how these distributions can show you where to improve your running. It would be nice if Stryd would give a comparison based on Critical Power, so you could compare with faster, fitter runners. I'd love to know how elites run at slow paces, and how their slow pace compares with mine.
[[File:Stryder Distribution.png|center|thumb|400px|Stryder Distribution]]
=Power to Heart Rate=
The relationship between your heart rate and your power output tells you how fit you are. This metric, [[HrPwr]], will go up as your fitness improves. Your HrPwr will also change during a run, with fatigue, dehydration, and [[Glycogen]] depletion all reducing your HrPwr as your heart rate drifts upwards.
=Testing Running Power Estimate=
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.
==Analysis of Power Estimate==
I've not performed any statistical analysis of Stryd's power estimate, mostly because I can't work out a reasonable way of doing this. Ideally, I'd be able to compare Stryd's power estimate with VO2 measurements from respiratory gas exchange, but I don't have the equipment, nor is it likely to be practical. The approach I've used above is to compare Stryd's power estimate with heart rate, but while heart rate is a well-established method of measuring exercise intensity, it's flaws (as noted in detail below) me know that he can only be used for relatively short periods of steady state exercise. (I'm hoping that someone will come up with a portable VO2 meter that will measure oxygen and carbon dioxide in your breath.)
=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.
