The objective assessment of physical activity in an occupationally active group

Thirty-five male United States postal carriers, mean age (+/-SD) 46.1 +/- 11.4 years, mean distance walked on the job 5.3 +/- 3.3 miles day-1, participated in this study to determine the efficacy of two movement sensors for the assessment of daily physical activity. Subjects wore both a Large Scale Integrated Activity Monitor (LSI) and a Caltrac portable accelerometer on a belt for 3 days (2 work days, 1 non-work day) for 2 separate trials separated by a 3 month interval. Both monitors indicated similar mean levels of physical activity over the 2 work days with a significant decrease on the non-work day. Test-retest reliability within one trial over the 2 work days (LSI, r = 0.64; Caltrac, r = 0.58) and and between 2 trials (LSI, r = 0.58, Caltrac, r = 0.57), were similar for both monitors. The mean values for the LSI and Caltrac over the 2 trials were highly related (r = 0.75). Analysis of variance indicated a high percentage of the total variance in physical activity was accounted for by interindividual differences for both monitors (LSI = 77.4%, Caltrac = 77.7%). These results suggest that both the LSI and the Caltrac provide a reliable index of physical activity and can detect inter-individual differences in activity level in occupationally active individuals.