Purpose: 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.
Methods: 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.
Results: 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.
Conclusion: 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.