Comparison of energy expenditure in normal-weight and overweight women using the Caltrac Personal Activity Computer

Researchers have been unable to discern the relationship between energy expenditure and obesity because there has been no reliable, unobtrusive method to capture daily activity. The Caltrac Personal Activity Computer (Caltrac) is a small, portable accelerometer that translates motion into activity counts when worn by human subjects. It has shown high test-retest reliability during laboratory trials and has demonstrated a strong relationship to several measures of energy expenditure in some laboratory tests. In order to correlate activity with amount of body fat, 39 university women (mean age = 19.15 years, mean weight = 135 lb, SD = 27.17, range = 100-220 lb) wore Caltracs for either 3 (n = 39) or 6 (n = 26) consecutive days. Pearson product-movement correlation coefficients showed a moderate negative relationship between Caltrac counts and body mass index (BMI) (r = -.47, p < or = .01) for Days 4-6 in the subjects who wore the Caltrac for 6 days, but there was no correlation between Caltrac counts and any measures of body fat for the first 3-day period.