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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, 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. 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. 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=
* '''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 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 that Stryd is underestimating my vertical oscillationcompared with other devices. However, which is perhaps not a surprise given this is only a mathematical model. Stryd suggests that this is because they are measuring the vertical movement of the runners' center of gravity rather than just the torso, but the research suggests that should which is a more appropriate and useful measure. Look for Fredrik Zilléns' excellent video "[https://youtu.be no difference between the two measurements while /pvt0lzvXTxc?si=5kHFHFWpp2t1Au_K Up/down movement when runningis 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.
==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.)
=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.) This is fascinating information, and quite intriguing, but like a lot of running metrics, it's hard to know how to use it. The footpath could be more useful if there was a reference path shown for a "good runner" that is running at your pace. Ideally, the tool would point out any actions you could take to improve your running automatically.
=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.
=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.