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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. At $200 220 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. (Note that you need to have access to an iOS or Android device to setup Stryd.)
{{BuyStryd}}
=The Metrics=
Stryd provides an array of different metrics, which vary both in accuracy and usefulness.
* '''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 altimeter'saltimeters. 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 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.
Note that Stryd provides no information on foot strike parameters such as pronation, or foot landing position.
=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 cablesthrough a small cradle (earlier versions used wireless charging. ) 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 IPX7Stryd claim IP67 waterproofing, which is submersed safe for submersion to 1 meter for up . However, that means that you can't run through water as the pressure due to 30 minutesfoot movement will exceed the pressure. That should be fine for nearly any running activity; would mean taking the pod off if you're more than ankle deep in going through water for more than 30 minutes then that will cover the pod, though I suspect you should be okay if you're having a bad timewalk through slowly.
<gallery widths=300px heights=300px class="center">
File:Stryd Wind (21).jpg|The pod has an LED on top (the white area in near the middle) that's used to convey status.File:Stryd (3).jpg|Here's The charging cradle is not much bigger than the Stryd pod on the shoe.File:Stryd Charging.jpg|Stryd , which is my first device that supports wireless chargingnice for travelling.File:Stryd Wind (1).jpg|I don't normally show packaging but the design is so minimalist yet elegant that I thought it was worth a picture. File:Stryd Comparison (12).jpg|Here's a visual comparison with some other Footpod's. From top left to bottom right there is the Stryd, Garmin Footpod, [[MilestonePod]] v3, Polar Sensor, Adidas, and [[MilestonePod]] v2.File:Stryd Comparison (3).jpg|This is a view of the Stryd and Garmin Footpods with their cradle to clip into pod on the shoe laces.File:Stryd Comparison (2).jpg|Looking sideways you can see the Stryd and Garmin Footpods have similar openings for shoe laces.
</gallery>
=Testing Running Power Estimate=
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.
==Bluetooth or Ant+==
Stryd supports both Bluetooth and Ant+, and both work well. Bluetooth has the limitation that you can only have one receiver talking to Stryd at a time, so you can't have it linked to two different watches simultaneously, or to a watch and your smart phone at the same time. (I have had occasions where the Stryd has stayed linked to my smart phone, so I've had to turn off Bluetooth on my phone to allow Stryd to link to a watch.) With Ant+ you can have as many watches linked simultaneously, and it's possible to have Stryd linked to both one Bluetooth watch and several Ant+ watches at the same time. If you're using Garmin [[Connect IQ]], you can have Stryd work as both a standard Footpod and connected via the Connect IQ data field.
=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. (If you're verifying a previous calibration, leave it set to that value but remember to adjust in the final calculations.)
* Use a standard 400 m oval track at a time when you're confident you can run in a single lane for a number of laps. The accuracy of a 400m track should be more than adequate for calibration, but if you're interested in the details, tracks are built in the US to various levels, with level 4 being suitable for national collegiate events.
* You should run approximately 30cm/12" from the inside edge of the lane, not down the middle. For the first lane, running along the inside marker will reduce the distance by ~1m, running the outside edge will increase the distance by ~3m, and running down the middle will increase the distance by ~1m.
* You don't have to run down the first lane, but you have to adjust your distances for lanes that are farther out. (See table below.)
* Start your watch and start running some distance before the start line. I would suggest at least 100 m. This is partly because the stride will do some smoothing, and obviously when you're run starts you're going from stationary to running. However, I've also noticed a number of watches that can be slow to start recording, so there first lap is rather short. You'll need to discard this first lap.
* Run a number of laps hitting the lap marker as you parse the start, or some other landmark.
* After the run, look at the lap distances for the measured laps, ignoring the first. The calculation is then fairly trivial; divide the actual lap distance by the average lap distance to give your calibration factor.
{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"
! Lane
! Total length
|-
| 1
| 400.00 m
|-
| 2
| 407.67 m
|-
| 3
| 415.33 m
|-
| 4
| 423.00 m
|-
| 5
| 430.66 m
|-
| 6
| 438.33 m
|-
| 7
| 446.00 m
|-
| 8
| 453.66 m
|-
| 9
| 461.33 m
|}
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.
==Example Calibration Data==
I ran a calibration test on a university track, running in the third lane with my Stryd on the inside (left) foot. I not only wanted to validate the calibration, but I also wanted to check the stability across a range of paces, so I gradually increased my speed on each lap. My previously calculated calibration was 1.013x (or 101.3% in my Garmin) and the average error was 100.15%, so my new calibration was 1.013 / 1.0015 = 1.011507, which works out to 101.2% on my Garmin.
{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"
! Distance (m)
! Ratio
! Error
! Avg Pace
! Best Pace
|-
| 414.8
| 0.998724
| -0.53
| 9:40
| 8:17
|-
| 414.1
| 0.997038
| -1.23
| 9:40
| 9:13
|-
| 416.7
| 1.003299
| 1.37
| 9:14
| 8:59
|-
| 414.8
| 0.998724
| -0.53
| 8:59
| 8:24
|-
| 416.3
| 1.002335
| 0.97
| 8:33
| 8:17
|-
| 414
| 0.996798
| -1.33
| 8:31
| 8:09
|-
| 415.8
| 1.001132
| 0.47
| 8:03
| 7:49
|-
| 417.4
| 1.004984
| 2.07
| 7:46
| 7:34
|-
| 417.2
| 1.004502
| 1.87
| 7:31
| 7:21
|-
| 415.5
| 1.000409
| 0.17
| 7:12
| 7:00
|-
| 416.4
| 1.002576
| 1.07
| 6:46
| 6:32
|-
| 417.2
| 1.004502
| 1.87
| 6:34
| 6:18
|-
| 417.9
| 1.006188
| 2.57
| 6:10
| 5:51
|-
| 415.1
| 0.999446
| -0.23
| 5:41
| 5:02
|}
=The Stryd App=
The Stryd app is rather limited, and I mostly use it just to sync data with the web site. It is needed for use on a treadmill. See below under "smartphone apps" for more details.
* '''Form Power, Ground Contact Time, Vertical Oscillation, Leg Stiffness'''. These fields are all available via the Garmin [[Connect IQ]] data field, and can be viewed using Garman Connect.
[[File:StrydGarminConnect.png|center|thumb|500px|A view of the data collected using the Garmin [[Connect IQ]] data field with Stryd also connected as the Footpod, using a [[Garmin Fenix 3]].]]
=Stryd and Running Economy=
One advantage of Stryd is that it's power estimate can be used to then estimate [[Running Economy]] and [[Heart Rate Drift]]. You can read more about this at [[HrPwr]].
=Testing Distance and Pace=
I tested the distant accuracy of the Stryd using the same basic methodology as I do for my [[GPS Accuracy]] testing. (See [[GPS Testing Methodology]] for details.) I used a [[Polar M400]] configured to use the distance from the Stryd footpod. As you can see from the results, the Stryd is remarkably accurate, far better than any GPS device I've tested. My testing of pace is more anecdotal, but I've been able to hit my target paces using guidance from my Stryd. I've tested using a range of paces from 10:00 min/mile to 6:30 min/mile and the Stryd allows me to cover a given distance in just the right time.
==Accuracy Walking==
I've not done any statistical analysis of the accuracy of the Stryd while walking, mostly due to time constraints. However, my anecdotal use of Stryd while hiking on my testing course suggests that it's equally accurate when hiking in boots as it is when running.
==Accuracy and Consistency at Different Paces==
My testing showed that Stryd remains consistent across a wide range of paces. I tested from 9:40 min/mile to 5:40 min/mile with no differences.
==Responsiveness ==
Stryd seems reasonably responsive to changes in pace, though it's hard to determine how the smoothing of Stryd interacts with any smoothing of the watch. I've found Stryd responds within a few seconds, though the power estimate is a little slower to adjust. Recent firmware updates have improved the responsiveness of the power estimate, though it's still a little slower than I'd like on rapidly changing slopes.
=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 main problem is my treadmill was speed display is way 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]].However, this variation makes it tricky to know what the "true" speed should be. Obviously, the average speed of the belt is completely wrong, as the speed of the belt while your airborne has nothing to do with your running speed. During the time your foot is in contact with the belt, should you use the minimum speed, the average speed or the maximum speed? With my treadmill, the difference between minimum and maximum during contact is about 15%, and between average and minimum is about 9%. I've found Stryd seems to be quite close to the minimum speed rather than the average during contact. I calibrated my treadmill and then calibrated Stryd to the corrected treadmill speed, which is a lot of effort and tricky to get right. A much simpler solution is to use the [[North Pole Engineering Runn Treadmill Sensor]], which measures the treadmill speed with far less effort and greater accuracy. [[File:Treadmill During Contact.jpg|center|thumb|300px|Treadmill speed during contact with the belt.]]
=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.
The claimed battery life for Stryd is only 20 hours, which is not long enough for many ultramarathons. Obviously, if you could have two Stryd pods, but that would be expensive. One option would be to use a Garmin watch that supports UltraTrac to extend the battery life along with the Stryd for accurate distance and pace. This would last for around 20 hours, and when the Stryd battery is dead, things would fall back to GPS. You may even be able to switch to normal GPS mode mid-run. I found that this worked nicely on a short run when I tested it out with the [[Garmin Fenix 3]]. I started off with the watch in UltraTrac mode and the Stryd connected. I then took the Stryd pod off to simulate the battery running out, and swapped to normal GPS mode.
[[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.]]
=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.)
[[File:Stryd Internals Paul Day.jpg|center|thumb|300px|Stryd Internals (Copyright Paul Day, used with permission.)]]
=Stryd and Critical Power=
The Stryd app has started to support [[Critical Power]], a concept more widely used in cycling. The Stryd method of calculating Critical Power is to use one of 5Km/10Km race time, or a test protocol using just two durations. The research I've found on Critical Power suggests that more data points are needed to provide a valid measure of Critical Power, and especially W' (anaerobic work capacity). Most research uses a fixed power output to exhaustion rather than a time trial. A time trial includes aspects of pacing and skill, so this seems a poor substitute. (Typically, CP tests define "exhaustion" as when cycling cadence drops below 50 RMP.) I'd recommend using more test runs and using one of the many Critical Power calculators available online. Stryd also has an [https://blog.stryd.com/2019/07/09/introducing-auto-calculated-critical-power/ automatically calculated Critical Power], but I've not seen any independent validation.
=Stryd's Power Estimate Compared with Cycling Power=
I performed an incremental test with both Stryd for running and my Tacx Neo 2 for cycling. For running, I used a 400m track, increasing my pace from 10:00 min/mile to 5:30 min/mile over 14 laps. I then performed a similar test cycling, increasing the power gradually. I then mapped the power from each to my heart rate. In both cases I found a reasonable linear relationship between power and heart rate. Using the linear relationship, I found that Stryd power is generally quite a bit higher than Cycling power. For me, Stryd Power = (Cycling Power + 40) / 1.13, so 100w in Stryd is about 70w Cycling.
=Using Stryd With Your Watch=
Here's my notes on the compatibility testing I've done so far. I've had occasional issues with devices connecting to Stryd at the beginning of a run. I've not found any pattern to this, and it seems to impact both Bluetooth and Ant+ devices, so make sure you have a connection before starting your run. I've also occasionally forgotten to turn off auto-calibrate, which is another gotcha.
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]]:
