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The purpose of this study was to determine the reliability and validity of the Fitbit® Charge 2™ compared to a 4-lead ECG to monitor heart rate during exercise. All participants completed a VO2Max test to determine the participants’ cardiorespiratory fitness and appropriate work loads for the intensity protocol. Participants wore a Fitbit® Charge 2™ on the wrist and a 4-lead ECG. 16 participants were assigned to testing conditions: GPS stride length/manual stride length and hold/no-hold on the handrails of the treadmill. The participants completed a walking protocol including light (60% of HRR) intensities while wearing both devices. Intraclass Correlation Coefficient (ICC) was used to analyze the results. The ECG is a reliable and valid means to monitor heart rate. The Fitbit® Charge 2™ demonstrated poor reliability and validity to monitor heart rate.