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Apple Watch: Validity of Exercise Metrics and Usability, an Extreme Endurance Cyclists’s Perspective

re: Apple Watch

I have used professional-grade gear for ~15 years for road cycling, eg my lab-grade (±0.5%) strain-gauge SRM Power Meter. Up to 12000 miles and 1.25 million vertical feet in a single year, 55 double centuries, etc.

That’s about as extreme as it gets for exercise. Accordingly, the bar is very high for what I expect in a tracking device for exercise. Still, I accept something in the range of ±5% for a wristwatch type device, so long as that level of precision holds (see precision and accuracy). Precision is far more important than accuracy for such things.


Exercise interface has no stop button I coudl figure out, I ended up with 10 segments, some caused by my wrist just bending because the band has to be tight. What a problematic interface. I have a lot of learning to figure out how to use the thing; it’s inherently much harder than a phone, with miniscule icons. I’ll need to remove the crapware and reconfigure it to make it usable.

Heart rate (bpm)

To get accurate heart rate, Apple Watch has to be strapped on fairly tightly (mildly uncomfortable), as I found when it was a little loose (reasonably comfortable)—a little loose and the HR runs 7-10 beats too low and is flaky.

I monitored both systems while cycling: strapped tightly, Apple Watch HR bpm matches my Polar H10 heart rate monitor strap beat-for-beat. A little loose and all bets are off, low and flaky readings.

UPDATE 1: in spite of claims, the Apple Watch will NOT see or pair with my SRM Power Meter, which makes the watch a dilettante toy for serious road cycling—power (watts) is the most important training metric, crucial.

UPDATE 2: since I want heart rate on my SRM Power Meter, I have to wear the Polar H10 heart rate strap. As it turns out, pairing that to the Apple Watch then gives identical heart rate recording to both. So at least for road cycling, I might as well not use the Apple Watch heart rate and instead use the reliable and more accurate Polar H10 data.

Altitude and ascent

Altitude with GPS units has hugely improved over the years, and the Apple Watch also has barometric altimeter. Dunno how it reconciles the two. Altitude seems spot-on at home. In the mountains... TBD.

As for total ascent (the metric most important to me after elevation), I need more experience to weigh-in on Apple Watch precision and accuracy.

Distance / speed / elapsed time

In a straight line, a good match for my extremely accurate bike readout (±0.5% or so, based on wheel revolutions with precise circumference configuration but tire pressure can vary slightly).

Where GPS distance works poorly is on road sections and hikes where the road/trail twists/turns, canyons, etc. Then the distance/speed can be pretty bad—as bad as 20% off.

Power (watts)

The Apple Watch will not even see the SRM Power Meter as available, so that information cannot be incorporated into the workout. It can pair with the Polar H10 heart rate monitor strap however.

Failure to account for active vs not

My SRM power meter knows when the bike starts and stops, it starts and stops automaticaly, and I configure it to not average-in that stopped portion.

The Apple Watch does not know any of this, so it averages in crap, making the statistics useless. And you have to manually start it. Yeah, you can do all the work of intervals (“segments”)—if you remember every start stop—which is no good if you just pull over for a drink in the middle of some other segment. Totally sucks as a pro tool—no time for that shit, particularly at mile 137 or whatever.

Crappy interface and viewing for cycling

Control over what is displayed is poor—one display, impossible to toggle while riding. On the SRM PC8 head unit, I have far more detailed and configurable data readout, and at an angle to my eye that I can actually read without contorting my wrist/hand position

Since the Apple Watch must be on the wrist (unless you wear a heart rate strap and pair it), you cannot really see the damned thing without contorting.

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