Latest revision as of 11:57, 16 January 2018

Garmin's Running Power Meter is a software download for their existing hardware, rather than a new hardware product. The software for Garmin Running Power (GRP) is their Connect IQ data field, but unfortunately, it won't run on any Connect IQ enabled Garmin watch. In fact, it will only run on the Garmin 935, Garmin Fenix 5X, and Garmin Chronos. (It supports the Fenix 5/5S, but those models appear to have hardware issues with sensors.) You also need a sensor that supports Garmin's Running Dynamics, which is available embedded in a heart rate strap or a clip-on pod. To get any meaningful data out of GRP, you'll also need a Footpod, preferably Stryd (more on that later.)

1 How It Works

Like any other running power meter, GRP estimates power primarily from your running pace and the slope. Running intensity is proportional to pace, and generally proportional to incline, but the relationship between intensity and running downhill is rather more complex. GRP claims to use three other factors:

• Vertical Oscillation. It seems intuitively obvious that the effort of bouncing up and down needs to be included in a running power, the science doesn't back this up. The relationship between vertical oscillation and effort (Running Economy) is not really valid. This is because the balance of a runner is more like bouncing a ball; there's some effort involved, but there's also a lot of elastic bounce as well.
• Breaking. Garmin referred to this as "horizontal oscillation" though most Running Sensors referred to this as the braking force. Strangely, Garmin's running dynamics system doesn't report on any braking force, though obviously it's able to detect horizontal acceleration.
• Wind. Generally, air resistance is incorporated through pace, but Garmin actually attempt to include wind speed. Their approach is to get with the data from a local weather station using the Bluetooth connection to a smart phone, and then use the heading to calculate your current windspeed. You'll need your smart phone with you, and it's possible that this approach might work in some very limited situations. You do need to be running in an environment where there's little or no shelter from the wind, such as trees or buildings, so that your subject to the prevailing winds. The wind would need to be steady in both direction and velocity. This combination of events seems to be so limited that I'm struggling to see any benefit. Luckily, you can turn this feature off.

2 Testing Results

I'm still testing GRP, but here are my initial thoughts.

• Getting your running pace from GPS is fairly useless, so it's not surprising that GRP's power estimate when using GPS as the speed source is pretty worthless. I typically see power estimates fluctuating by +/- 50 watts when maintaining an even effort.
• When I use Stryd as a Footpod to provide current pace, GRP provides a much better power estimate than with GPS (no surprise.)
• On the flat, GRP provides a reasonable power estimate that varies with pace as you'd expect.
• On the transition from flat to uphill, GRP seems to lag more than Stryd. So, if you keep a constant intensity/heart rate when you go from the flat to an incline, GRP will drop its power estimate in response to the slower pace, before it compensates for the incline and returns the power estimate to an appropriate level.
• On uphill sections, GPR mirrors Stryd fairly closely.
• On transition from flat to downhill, GRP suffers a similar lag, this time as a spike in estimated power.
• On downhill sections, GRP does particularly badly, underestimating effort fairly consistently. This was a problem Stryd initially had, but they have mostly corrected the problem. I expect GRP to get better at downhill power estimates, though this is a tricky problem to solve. While there is some research into the "U" shaped curve between V̇O₂ and decline angle, I strongly suspect the curve is highly individual.
• I've not tested GRP with a Garmin Footpod, but this might be a more cost-effective approach then using Stryd. Of course, it will also require a lot more effort in terms of regularly recalibrating the Footpod, something you don't have to do with Stryd.
• The GRP estimate of power is much higher than the estimate I get from Stryd. Garmin claim that running power should be higher than cycling power for a given effort based on a number of research papers. I've reviewed this research in my Running Power Meters article and it appears completely flawed. The good news is that you can simply enter your weight into Garmin as about 2/3rds your real weight to get more useful data.
• Because GRP is a Connect IQ data field, you can have it concurrently with the Stryd data field. Neither of them will record it to the standard power track in an FIT file, which means they both require some software support. Golden Cheetah supports Stryd power track natively, but doesn't yet support GRP. My workaround is to use SportTracks desktop app with the custom data tracks plugin, which allows me to copy the Connect IQ power data into the standard power data fields and then export it.

A comparison of Garmin Running Power (GRP) and Stryd's power estimate.