Comparison of pedometer and accelerometer measures of free-living physical activity

Purpose: The purpose of this investigation was 1) to evaluate agreement between dual-mode CSA accelerometer outputs and Yamax pedometer outputs assessed concurrently under free-living conditions; 2) to determine the relationship between pedometer-steps per day and CSA-time spent in inactivity and in light-, moderate-, and vigorous- intensity activities; and 3) to identify a value of pedometer-steps per day that corresponds with a minimum of 30 CSA-min.d(-1) of moderate ambulatory activity. Methods: Data were analyzed from 52 participants (27 men, 25 women; mean age = 38.2 +/- 12.0 yr; mean BMI = 26.4 +/- 4.5 kg.m(-2)) who were enrolled in the International Physical Activity Questionnaire study and wore both motion sensors during waking hours for 7 consecutive days. Results: Participants averaged 415.0 +/- 159.5 CSA-counts.min(-1).d(-1), 357,601 +/- 138,425 CSA-counts.d(-1), 11,483 +/- 3,856 CSA-steps.d(-1), and 9,638 +/- 4,030 pedometer-steps.d(-1). There was a strong relationship between all CSA outputs and pedometer outputs (r = 0.74-0.86). The mean difference in steps detected between instruments was 1845 +/- 2116 steps.d(-1) (CSA > pedometer; t = 6.29, P < 0.0001). There were distinct differences (effect sizes >0.80) in mean CSA-time (min.d(-1)) in moderate and vigorous activity with increasing pedometer-determined activity quartiles; no differences were noted for inactivity or light activity. Approximately 33 CSA-min.d(-1) of moderate activity corresponded with 8000 pedometer-steps.d(-1). Conclusion: Differences in mean steps per day detected may be due to differences in set instrument sensitivity thresholds and/or attachment. Additional studies with different populations are needed to confirm a recommended number of steps per day associated with the duration and intensity of public health recommendations for ambulatory activity.