I am interested to see whether I can put my Stryd aside and switch to Garmin power instead.
I performed a simple treadmill test of Wrist Power vs HRM Pro Power. I have 3 laps of 1mn with the treadmill set at 7mph or 8:32mn/mi.
Lap 8 is wrist only, both for power and pace
Lap 12 is HRM Pro only, both for power and pace (note that the HRM Pro was automatically calibrated by the watch)
Lap 14 is HRM Pro for power, but Stryd for pace (note that Styd was accurately manually calibrated on a track)
Before pressing the lap button, I made sure that (a) the treadmill had reached the target speed, and (b) ran for an additional 15s buffer.
As you can see below, the HRM Pro power reading is noticeably higher than the wrist-based power: between 53W (w/ Stryd-based pace) and 70W (w/ HRM Pro-based pace).
Stryd Pace was the closest to the treadmill reading. The Wrist pace was the worst (much slower). The HRM Pro pace reading was significantly faster than actual.
From the math, most of the power differences can be explained by pace reading differences. Here are the power and speed ratios to compare the laps. I use Lap 14 as the reference, since this lap recorded the most accurate and stable pace with Stryd.
| Lap x / Lap 14 | Avg Speed ratio | Avg Power ratio |
| 8 (wrist) | 0.857 | 0.835 |
| 12 (HRM Pro) | 1.057 | 1.049 |
| 14 (HRM Pro + Stryd for pace) | 1 | 1 |
If the average pace was the only factor, the power for lap 12 would be 1.057 times the power of lap 14, or 346W, which is very close to the actual 343W value (0.87%). Using the same approach for lap 8, if pace was the only difference, the power would have been 0.857 times the power of lap 14, or 280W, which is very close to the actual 273W (2.5%). I am attributing the differences to lap execution differences (form power, for example, or wrist movement to press the button)
The Stryd Power was very stable and consistent at ~235W, with +/- 1W fluctuations during the interval (not represented above), to be compared with Lap 14 average power of 325, putting Garmin HRM Pro power 1.38x higher than Stryd Power. Some other testers reported about 33%, so maybe this is again due to the lack of adequate calibration of the HRM Pro in my test.
Unfortunately, the HRM Pro UI doesn't allow for a manual calibration input (like for the Stryd Pod).
I am surprised to see significant variations of pace from the HRM Pro during the 1mn interval. The next step for me is to run again longer outdoors to give auto-calibration a second shot, and then longer intervals on the treadmill to evaluate the stability and consistency of the HRM Pro pace.
