Horton JF, et al. – An assessment was pursued of the accuracy of the Polar M600 optical heart rate (OHR) sensor compared to ECG heart rate (HR) measurement during various physical activities. The data determined that Polar M600 was accurate during periods of steady state cycling, walking, jogging, and running, but less accurate during some exercise intensity changes. This was possibly due to factors associated with total peripheral resistance changes and pulse pressure.