Beyond Cut Points: Accelerometer Metrics that Capture the Physical Activity Profile

Purpose Commonly used physical activity metrics tell us little about the intensity distribution across the activity profile. The purpose of this paper is to introduce a metric, the intensity gradient, which can be used in combination with average acceleration (overall activity level) to fully describe the activity profile. Methods A total of 1669 adolescent girls (sample 1) and 295 adults with type 2 diabetes (sample 2) wore a GENEActiv accelerometer on their nondominant wrist for up to 7 d. Body mass index and percent body fat were assessed in both samples and physical function (grip strength, Short Physical Performance Battery, and sit-to-stand repetitions) in sample 2. Physical activity metrics were as follows: average acceleration (AccelAV); the intensity gradient (IntensityGRAD from the log–log regression line: 25-mg intensity bins [x]/time accumulated in each bin [y]); total moderate-to-vigorous physical activity (MVPA); and bouted MVPA (sample 2 only). Results Correlations between AccelAV and IntensityGRAD (r = 0.39–0.51) were similar to correlations between AccelAV and bouted MVPA (r = 0.48) and substantially lower than between AccelAV and total MVPA (r ≥ 0.93). IntensityGRAD was negatively associated with body fatness in sample 1 (P

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