Comparison of step outputs for waist and wrist accelerometer attachment sites

Purpose: The objective of this study is to compare step outputs obtained from waist and wrist accelerometer attachment sites under laboratory and free-living conditions. Methods: Under the laboratory condition, participants concurrently wore ActiGraph accelerometers at their waist and nondominant wrist while walking/ running at treadmill speeds between 14 and 188 mIminj1. Visually counted steps served as a criterion standard. Participants then wore both accelerometers for 7 d. All accelerometer step data were processed applying both the manufacturer's default and low-frequency extension filters. Paired sample t-tests were used to evaluate mean differences in criterion steps per minute and the four (attachment site × filter) estimates produced from the waist- and wrist-worn accelerometers in the laboratory study. Free-living differences in mean steps per day detected between the waist and wrist (considering both filters) were computed. Results: Relative to visually counted steps, the waist attachment site generally outperformed the wrist attachment site at most speeds, regardless of the applied filtering process. Under free-living conditions, the waist-worn accelerometer detected 6743 × 2398 (default filter) and 13,029 × 3734 (low-frequency extension) steps per day. The concurrently worn wrist accelerometer detected 9301 × 2887 (default filter) and 15,493 × 3958 (low-frequency extension) steps per day. Conclusion: The wrist attachment site detected consistently fewer visually counted steps than the waist attachment site at most treadmill speeds during laboratory testing. In contrast, the wrist attachment site produced a higher average step count (ranging from approximately 2500 to 8700 more steps per day under free-living conditions, dependent on the filtering process applied) than the waist attachment site under free-living conditions. In conclusion, step outputs obtained from waist- and wrist-worn accelerometer attachment sites are generally not comparable under either laboratory or free-living conditions.