The general inaccuracy of wrist based heart rate monitors
One of the things that I am aware of is the inconstancy of wrist-based heart rate monitors, which is obviously what Whoop uses. I became acutely aware of this several years back when I purchased a Suunto Spartan. Now off the bat, I will say that I love this watch. I take part in a wide variety of outdoor activities and like the GPS tracking, especially for winter mountain-based activity. But when it came to the HRM, let’s just say it had some issues… lf during a trail run my actual heart rate was close to what the readout was? I would be too dead to write this blog. The fact that this would happen on all runs was the only consistent thing about the HRM on the Suunto Spaartan. Skiing it would be off, not as much as a run but more than a bike ride. And a mountain bike ride was likely more scattershot than a gravel ride. I was able to come to this general conclusion through the use of an Apple Watch… yes with its flaws. But eventually with a chest strap connected to the very same Suunto Spartan. But that doesn’t mean the Apple watch was any better. Bottom line is that when I compared wrist based readings with any chest strap or finger at my neck. There were inconsistencies. If they were percentage consistent you could make up for it, but they weren’t and you couldn’t.
My good friend Matt over at Endurelite posts regular “60-second brain bombs” where he drops some knowledge on you in an entertaining fashion. Back in May of ’20, he posted a video about HR on a wristwatch. Not surprisingly he points to a study that showed that the typical watch was off by anywhere from 29-39%, and suggests that if HR is an important part of your training you should wear an HR with the chest strap. Matt’s video can be seen here. Luckily for me HR doesn’t factor into my outdoor activities as I don’t train, I enjoy. I’m interested in those watches more for the other features of tracking, specifically the GPS for things like speed and distance.
Whoop as a heart rate monitor
The test was all with watches and did not include a Whoop. But that got me thinking if the basis of Heart Rate Variability is heart rate… I mean it’s right there, two of the three words. Then how would a similar issue with the Whoop affect results? I worked out in my head that if the basis were variability then the impact might be negligible as the inconsistency would carry across the board and be consistent… yes, I get the irony. And if it were consistent it would still be similarly measuring the day-to-day. One thing right off the bat was that the Whoop was not erratic so that was good. I ‘tested’ it against my Apple Watch and Suunto Spartan with the chest strap and found the Whoop to be closer to the chest strap than the Apple Watch, but still not accurate. Quick disclaimer, this is assuming two things. That the chest strap and specifically with the Suunto is indeed the more accurate and that Apple has not improved on the older model I have. Now as for ‘tested’. I walked the dog, sat around, ran a bit, and rode a little… This is no UL listing service here. During the sitting around portion of my ‘scientific test’, I searched to see if anyone with more knowledge than me had looked into the accuracy of the Whoop. I came across this great blog by Michael Kummer that definitely worth the read.
If you don’t have the time to read another linked piece let me share this from the article, “Based on my use cases and requirements, the WHOOP wearable is accurate in the areas that matter most to me. That includes recovery and sleep tracking.” And that is what I’ve been coming to over the last 20 days. Wrist-based HR tracking seems to be affected by the ‘noise’ generated during activity as well as potential flaws in processing and other variables. Theoretically, it should still track well during sleep and recovery. Since I’m not training and am looking for some statistical information to help me perform better across the entirety of my life I still think this is a good fit.