Validity of Physical Activity Monitors in Assessing Energy Expenditure in Normal, Overweight, and Obese Adults

A comparison of the validity of downloadable motion sensors, which use either a glass-enclosed magnetic reed proximity switch technology, a piezo-electric sensor accelerometer with a horizontal beam technology, or an internal pendulum based mechanism to determine energy expenditure (EE), across different body sizes does not exist. Therefore, the purpose of this study was to determine the validity of three different downloadable motion sensors to estimate EE during walking activity in normal weight, overweight and obese volunteers. Forty-eight participants completed this study. Each participant had their body height and mass measured and completed a treadmill walking protocol. Body mass index (BMI) was calculated. The treadmill walking protocol included six 5-minute stages starting at 1.5 mph and increasing by 0.5 mph, up to 4.0 mph while grade was constant at 0% for the duration of the test. The Kenz Life-Corder EX (LC), the Omron HJ-700IT (OM) and the Sportbrain iStep X1 (SB) were worn during the treadmill walking protocol. Heart rate, oxygen consumption, carbon dioxide production and EE estimated from the motion sensors were monitored throughout the walking protocol. Results showed the OM overestimated net EE in normal, overweight and obese participants. The LC underestimated gross EE in all groups. The SB overestimated net EE in normal BMI participants, was not significantly different from the criterion measure of net EE in overweight participants and underestimated net EE in obese individuals. This study demonstrates that these devices do not offer the accuracy needed to provide precise feedback on EE for individuals with varying BMI levels.