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 exercise bout, the accelerometer readings (in arbitrary units) were recorded and expressed in counts per minute. The analysis of variance for the Calcount 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 less than .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 accelerometer readings ranged from -.09 to .49, indicating that the output of the two accelerometers cannot be compared directly.