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From Fellrnr.com, Running tips
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==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.
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However, it's also in indication of some of the weaknesses of mathematically estimating our rather than measuring it. If we look at the steep descent on the second hill, it looks like there is still some underestimation of power. The other possible issue is that Stryd is estimating for a typical runner, and each person's efficiency under different conditions is likely vary quite a bit. It's important to remember the limitations of this type of estimation, and avoid confusing it with what you'd get from a power meter.
[[File:Stryd LpV Descent.jpg|center|thumb|400px|]]
==Statistical 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.
[[File:Stryd And Ultratrac.jpg|center|thumb|200px|Here's the GPS track, and hopefully you can see the straight lines that you get when the watch is in UltraTrac mode and only checking GPS infrequently. On the way back I had normal GPS mode.]]
=Calibrating Stryd=
My testing shows that Stryd is remarkably accurate, but the company has reported that there can be some variation between Stryd devices. If you'd like to check your calibration, I'd recommend this process. (Note that the Suunto Spartan watches don't allow for any calibration.)
* Check that your watch is set to get pace and distance from Stryd. The best way I've found to verify this is to set the calibration factor to 0.5 and go for a short run. It will be immediately obvious that your pace is only half what it should be.
* Check the calibration factor is set to 1.0, and that any auto calibration is disabled. Auto calibration uses GPS, which is going to be far less accurate than Stryd.
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Don't use a race to calibrate, as it typically very difficult to precisely run a straight line and hit the tangents perfectly. You can also have problems with start up on some watches, where it doesn't record the first few seconds of the run.
=Stryd Internals=
For those that are interested, here are the internals of a Stryd. (Thanks for Paul Day for the photo and the willingness to do the work.)
For the [[Garmin Fenix 2]]:
* Pair as a normal footpod.
* Set the "Foot Pod Speed" to "Always On". I expected this to just provided provide pace from Stryd, but it actually does distance as well. The GPS track is recorded normally and navigation functions are enabled.
==Suunto Ambit3 (all models), Ambit2 R==
For the [[Suunto Ambit3]] (all models), [[Suunto Ambit2| Suunto Ambit2 R]]:
* Ensure you are using a sports mode that has the footpod enabled and the power pod disabled.
* Power data can be exported to tools like Golden Cheetah by exporting the FIT file from the Suunto web site (activity page, click on the tools on the right, select "export as FIT").
* There's no calibration provided by the Suunto Spartan.
==Garmin 620, 225, 610, 910XT, 310XT==
For the [[Garmin 620]], [[Garmin 225]], [[Garmin 610]], [[Garmin 910XT]], [[Garmin 310XT]]:
