Validity of four motion sensors in measuring moderate intensity physical activity

Purpose: This study tested the Validity of four motion sensors for measurin g energy expenditure (EE) during moderate intensity physical activities in field and laboratory settings. We also evaluated the accuracy of the EE val ues for selected moderate activities listed in the 1993 Compendium of Physi cal. Activities. Methods: A total of 81 participants (age 19-74 yr) complet ed selected tasks from six general categories: yardwork, housework, occupat ion, family care, conditioning, and recreation. Twelve individuals performe d each of the 28 activities examined. During each activity, EE was measured using a portable metabolic measurement system. Participants also wore thre e accelerometers (Computer Science and Applications [CSA], inc. model 7164; Caltrac; and Kenz Select 2) and the Yamax SW-701 electronic pedometer. For the CSA device, three previously developed regression equations were used to convert accelerometer scores to EE. Results: The mean error scores (indi rect calorimetry minus device) across all activities were: CSA1, 0.97 MET; CSA2, 0.47 MET, CSA3, 0.05 MET; Caltrac, 0.83 MET; Kenz, 0.96 MET; and Yama x, 1.12 MET. The correlation coefficients between indirect calorimetry and motion sensors ranged from r = 0.33 to r = 0.62. The energy cost for power mowing and sweeping/mopping was higher than that Listed in the 1993 Compend ium (P < 0.05), and the cost for several household and recreational activit ies was lower (P < 0.05). Conclusion: Motion sensors tended to overpredict EE during walking. However, they underpredicted the energy cost of many oth er activities because of an inability to detect arm movements and external work. These findings illustrate some of the limitations of using motion sen sors to predict EE in field settings.