Accelerometer response to physical activity intensity in normal-weight versus overweight African American children.

BACKGROUND Different movement efficiency in overweight children may affect accelerometer output data. The purpose was to investigate the ability of accelerometers to assess physical activity intensity and number of steps in normal-weight compared with overweight children. METHODS Eleven normal-weight and 14 overweight African American children walked at 2, 4, 5, and 6 km/h on a treadmill wearing Lifecorder, ActiGraph, RT3, and Biotrainer. Oxygen uptake was measured and steps manually counted. Fat free mass (FFM) was assessed from bioelectrical impedance analysis. Accelerometer counts and the individual linear regression lines of accelerometer counts versus VO(2)/FFM were evaluated, together with steps recorded by Lifecorder and Actigraph. RESULTS Correlations between accelerometer counts and VO(2)/FFM for all monitors were r ≥ .95 (P < .01). The accelerometer counts and their relationship to VO(2)/FFM did not generally differ significantly by body weight status. Lifecorder and Actigraph underestimated steps at 4, 5, and 6 km/h by less than 9%, but the error was up to -95% at 2 km/h. CONCLUSIONS All 4 accelerometers show high ability to assess physical activity intensity, and can be used to compare physical activity between normal-weight and overweight children. The Lifecorder and the ActiGraph showed high accuracy in assessing steps, providing speed of movement exceeded 2 km/h.