Ability of different physical activity monitors to detect movement during treadmill walking.

This study assessed the ability of four different activity monitors to discriminate changes in treadmill walking velocity. The relationships between walking velocity and bodily movement and between bodily movement and energy expenditure determined by indirect calorimetry (IC-EE or METs) were determined. Twenty-eight subjects walked at 3.2, 4.0, 4.8, 5.6, and 6.4 km/h (0 % grade) for 30 min on separate occasions. The Tritrac-R3D (TT), Computer Science & Applications, Inc. (CSA), and Mini-Logger (ML) activity monitors that measure bodily acceleration in one or three planes, and a Yamax Digiwalker-500 (YX) that records footsteps, were secured at the waistline of each subject. CSA monitors were also worn at the wrist and ankle. Walking velocity and bodily movement were significantly related (r = 0.89 to 0.93) for TT, CSA, ML, and YX. Importantly, changing each walking velocity produced significant changes in bodily movement that was detected by each monitor. Bodily movement and IC-EE were significantly related for TT, CSA, ML, and YX (r = 0.47 to 0.94). Compared to IC-EE, and at all walking speeds, EE was significantly overestimated by the TT, and EE was significantly underestimated by the YX. These results indicate that the activity monitors can differentiate bodily movement associated with walking at slow speeds better than they can estimate energy expenditure associated with walking at slow speeds.