2018/06/01 by ALEX V. ROWLANDS, CHARLOTTE L. EDWARDSON, MELANIE J. DAVIES +3 · 2 citations
paper · doi:10.1249/mss.0000000000001561
ABSTRACT 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 (Accel AV ); the intensity gradient (Intensity GRAD from the log–log regression line: 25-m g 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 Accel AV and Intensity GRAD ( r = 0.39–0.51) were similar to correlations between Accel AV and bouted MVPA ( r = 0.48) and substantially lower than between Accel AV and total MVPA ( r ≥ 0.93). Intensity GRAD was negatively associated with body fatness in sample 1 ( P P AV and potential covariates. By contrast, MVPA was not independently associated with body fatness or physical function. Conclusion Accel AV and Intensity GRAD provide a complementary description of a person’s activity profile, each explaining unique variance, and independently associated with body fatness and/or physical function. Both metrics are appropriate for reporting as standardized measures and suitable for comparison across studies using raw acceleration accelerometers. Concurrent use will facilitate investigation of the relative importance of intensity and volume of activity for a given outcome.