Changes

=The Pod=

The Stryd pod is similar to other Footpods. It's slightly larger than most, and has an LED status light on the top. Stryd uses a rechargeable battery that they claim lasts about 20 hours, though my testing indicates it lasts much less time. That's good enough for most runners, but may be a problem for longer ultramarathons. Stryd recharges wirelessly, which is nice, as I hate fiddling around with connectors or losing specialist cables. Stryd uses a 9-axis sensor rather than the typical [[Footpod]] that uses a 3-axis sensor. The Stryd pod weighs 0.32oz/9.1g, compared with the Garmin Footpod at 0.34oz/9.6g, and the rather oversized Polar Footpod at 1.0oz/28.1g. Stryd doesn't provide any details of the waterproof rating of their pod. With its wireless charging, I'd have expected it to be quite waterproof, but there are reports that it's IPX7, which is submersed to 1 meter for up to 30 minutes. That should be fine for nearly any running activity; if you're more than ankle deep in water for more than 30 minutes then you're having a bad time.

=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.

=The App=

The Stryd app is rather limited, and I mostly use it just to sync data with the web site. However, a key feature is to configure Stryd to transmit the power estimate in the Footpod's Cadence field. This feature is not currently supported in the Android version of the app!

=The Web Site=

I rather like the Stryd website. There's the usual calendar views of your runs, but there is some useful analysis you can do within their website. The biggest shortcoming I've found is that you can only show data by time, not by distance. If you look at the first graph below the hill shown by the purple line looks asymmetric because I'm going down much faster than I'm going up.

Stryd have added some analysis on their web site that looks at your overall training history. The heatmap is certainly fascinating, though I'm not sure how useful it is. It shows the highest power estimate you've run at for various times. The color then shows the how often you've achieved a power estimate/time combination. If you mouse over the line, you can see a popup with the details. You can see my curve is fairly flat, indicating my training intensity doesn't very much, which is what I'd expect given most of my training is [[Long Run]]s. I'm not sure how to interpret the Stryd Runner Profile or how it's calculated.

=Connect IQ Data Field=

The Connect IQ Data Field for Stryd will show power on a Connect IQ compatible Garmin watch. This doesn't interfere with using Stryd as the footpod at the same time, which is important. The Data Field will record not only power, but the other metrics like Ground Contact Time and the display is configurable to show power averaged over various time periods, lap average, or overall power for the run. Of course, you can only have one field configured, so you can't see both current power and lap average for instance. You also don't get alerts based on power value. If you put power into the cadence field you can do far more, adding current, lap average, alerts, etc.

[[File:StrydHardUpEasyDown.jpg|center|thumb|700px|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]].]]

Another interesting use for Stryd is to provide more even pacing on hilly courses. The graph below shows me attempting to keep an even effort based on the Stryd power estimate. My goal was to keep my intensity at about the same level as a running at 8:30 min/mile pace on level ground, which at the time of this run is about 200-210 watts and about 135-140 BPM heart rate. You can see that I was moderately successful, though both my heart rate and estimated power were a higher than my target. I was surprised by just how slow I had to go up the hill to compensate for the slope. You can see this more accurately in the lower image that's looking at the Stryd pace data. Even though my pace has dropped to 12:18 min/mile my heart rate and estimated power are both well above target. This means that to go up this hill with the same effort as 8:30 min/mile on the flat, I'd need to drop to quite a bit slower than 12:30 min/mile pace. Here the estimated power data is far more usable than heart rate, as I can tweak my pace moment by moment rather than waiting for my heart rate to adjust. I found that in practice, the Stryd estimated power output is remarkably effective at giving me real-time feedback of my exercise intensity on level ground and uphill. Though this is still a modeled, estimated power intensity, for uphill and level ground, it's far better than anything else available to us and is good enough for real world usage.

Sadly, things are not quite so rosy on the downhill sections. The graph below shows a hill repeat where I took it easy on the way up, and then pushed the pace hard on the way down. You can see that during the downhill section, my heart rate has risen a little, but the estimated power output has dropped massively. You can see my pace a little more accurately on the lower chart that uses the Stryd data, and my pace is hitting 6:30 min/mile. This matches up with my overall experience of Stryd, which consistently underestimates my exercise intensity for downhill sections of my run. This is a little limiting, as it means I come to use Stryd to pace myself when running downhill. I'm reasonably confident that Stryd will update their model to improve this, but it is currently a noteworthy shortcoming.

=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.