Factors Affecting Caltrac ® and Calcount® Accelerometer Output

This investigation determined the effects of different trunk levels and walking speeds on the output of two physical activity monitoring devices—the Caltrac® and the Calcount®. Twenty healthy subjects walked on a level motor-driven treadmill at two walking speeds (2 and 4 mph) with the accelerometer affixed to different trunk locations (waist belt and chest line). After each five-minute exer-cise bout, the accelerometer readings (in arbitrary units) were recorded and expressed in counts per minute. The analysis of variance for the Calcounf® accelerometer data revealed a significant main effect for location and speed. The Caltrac ® accelerometer data revealed a significant F ratio for the speed main effect and the location x speed interaction effect. Overall, the accelerometer reading when worn at the waist belt was higher (p <.05) than when affixed to the chest line. For both accelerometers, the output increased with increased walking speed. The correlation between the Caltrac ® and Calcount ® accelerom-eter readings ranged from-.09 to.49, indicating that the output of the two accelerometers cannot be compared directly