This morning was my second workout with a Whoop on my wrist. In both cases, Whoop's data is inaccurate and grossly overstates the intensity of the workouts. I recorded both sessions with the Whoop and a Garmin Fenix 2 with an HRM-Run chest strap.
Today's workout was a recovery session with an average heart rate of less than 60% of maximum. Despite being crazy-easy, the errors in the Whoop data (and the lack of any customization options for heart rate zones or thresholds) had this workout classified as "more strenuous than 96% of all days across Whoop athletes." I wish that were true...
I have unusually high heart rates at all intensities. This isn't due to fitness, but (as I understand it) low cardiac stroke volume. Compared to the average population, the size of my heart is smaller relative to body size. So it beats faster to keep up.
So without the option to correct for this, the Whoop software must use general averages and thinks I'm working harder than I am. It seems like an amateurish oversight on their part not to allow for customized thresholds.
In contrast, every other heart rate system I've used allows the user to set personalized heart rate zones or, better yet, an anaerobic threshold. Setting a personalized threshold would get rid of this type of error.
The second factor is likely the lower accuracy of an optical heart rate monitor (in the Whoop) compared to a chest strap monitor. To minimize this in future workouts, I've shaved my wrist and tightened the wrist strap. Hopefully that will help.
I was tempted to try Whoop because they recently changed their revenue model from exorbitant to merely over-priced. But if this imprecision continues, I hope that their return policy is as good as their marketing and graphic design.