Validity of the simultaneous heart rate-motion sensor technique for measuring energy expenditure

To determine the validity of the simultaneous heart rate-motion sensor (HR+M) technique for estimating energy expenditure (EE) by comparing it with indirect calorimetry. In addition, we examined the validity of the flex heart rate (FlexHR) method to estimate EE.

Ten participants (4 men: 26.7 yr +/- 1.5, and 6 women: 26.5 yr +/-3.3) performed arm and leg work in the laboratory for the purpose of developing individualized HR-oxygen uptake (VO2) regression equations. Participants completed physical tasks in a field setting while HR, VO2, and motion sensor data were collected on a near-continuous basis for 6 h. Accelerometers, one on the arm and one on the leg, were used to discriminate between upper- and lower-body movement. HR was used to predict EE (METs) from the corresponding laboratory regression equation. Predicted values (METs) were compared with measured values (METs) obtained via a portable metabolic measurement system.

The simultaneous HR+M technique showed a significantly stronger relationship with VO2 (R2 = 0.81, SEE = 0.55 METs) in comparison with the FlexHR method (R2 = 0.63, SEE = 0.76 METs) (P < 0.001). The FlexHR method significantly overestimated measured minute-by-minute EE (P < 0.001), whereas the simultaneous HR+M technique did not. The simultaneous HR+M technique accurately reflected time spent in resting/light, moderate, and hard activity, whereas the FlexHR method underpredicted time spent in resting/light activity (P = 0.02) and overpredicted time spent in moderate activity (P = 0.02). The simultaneous HR+M technique also accurately estimated total 6-h EE.

The simultaneous HR+M technique is an accurate predictor of EE during free-living activity and provides a valid measure of the time spent in various intensity categories.