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.

Link to Abstract: http://www.ncbi.nlm.nih.gov/pubmed/12471314