Are Wrist-based Heart Rate Monitors a Valid Tool for Fitness Professionals to Measure Training Intensity During Exercise Classes?

This article aims to inform personal trainers and group fitness coaches about the validity and utility of wrist-located heart rate (HR) monitors compared to chest-located HR monitors for training purposes. HR from four wrist-based optical sensor HR products (Fitbit Charge HR, Garmin Vivosmart HR, Apple Watch series 1, Mio Fuse) were compared against a Polar H7 chest strap & RS800cx receiver during nine activities. Two researchers visually observed HR during a protocol incorporating resting, standing, a grocery bag carry, and a 6-stage cycle ergometer protocol that reached maximal HR. Pearson’s r and interclass correlations (ICC) in the sample (n=45, mean age=20.22 [SD 2.32]) resulted in the following: Mio Fuse r=.93, ICC=.97; Apple Watch 1 r=.91, ICC=.95; Fitbit Charge HR r=.83, ICC=.91; and Garmin Vivosmart HR r=.74, ICC=.85 (all p’s <.001). Bland-Altman plots showed the lowest bias for the Mio (-3.30 bpm), followed by the Apple Watch (-2.82 (SD:14.6) bpm), Garmin (-2.99 (SD:23.9) bpm) with Fitbit having the highest bias (-8.13 (SD:20.6) bpm). No drift in bias was found for any device in successive HR categories (all p’s >.09). Wrist-based HR monitors were deemed acceptable for fitness classes, though caution should be taken when interpreting any singular visually observed measurement point. KEYWORDS: Smartwatch; Heart Rate Monitoring; Fitness; Fitness Watch; Validity; Exercise; Cycle Ergometer; Training; Intensity