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

Abstract

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