Is the Polar F6 heart rate monitor less accurate during aerobic bench stepping because of arm movements?

Because of the well-documented linear relationship between heart rate and oxygen consumption (VO2), heart rate is commonly used to estimate energy expenditure during exercise. However, previous research suggests that heart rate increases without a concomitant rise in VO2 when arm movements are added to exercise. If so, this could impact the accuracy of heart rate monitors in estimating energy expenditure during combined arm and leg exercise. This study compared the cardiorespiratory responses to a bench step aerobics routine performed with and without arm movements and evaluated whether the accuracy of the Polar F6 heart rate monitor in predicting energy expenditure was impacted by the inclusion of arm movements. Thirty-two women performed the same routine with and without arm movements while stepping up and down off of a 15.24-cm bench at a cadence of 128 b·min-1. Heart rate and VO2 increased, whereas oxygen pulse (VO2·heart rate-1) decreased when arm movements were added (p < 0.001). However, the differences between the energy expenditure estimated by the Polar F6 heart rate monitor and the energy expenditure measured by indirect calorimetry were similar during the same aerobic bench stepping routine performed with and without arms (Δ∼2 kCal·min-1, p ≥ 0.05). Results confirm that arm movements during aerobic bench stepping elicit a disproportionate rise in heart rate relative to V[Combining Dot Above]O2. However, results do not support that these movements increase the prediction error in energy expenditure, as the Polar F6 heart rate monitor over predicted energy expenditure when arm movements were involved and when they were not involved.