To inform the development of bone-specific physical activity (PA) assessment methods and contribute to bone-specific PA guidelines, accelerometer outcomes that provide the most valid estimates of skeletal loading in adults must be identified. Purpose: The aims of this project were twofold: 1) to assess the concurrent validity of raw accelerometer outputs with ground reaction forces (GRF) and loading rates (LR) calculated from force plate across a range of simulated habitual PA and 2) to identify the optimal wear site among the ankle, hip, and wrist with the strongest relationships between accelerometer and force plate and/or skeletal outcomes. Methods: Thirty healthy young adults (23.0 ± 4.5 yr, 50% female) wore a triaxial accelerometer at the right ankle, hip, and wrist while performing eight trials of walking, jogging, running, low box drops, and high box drops over an in-ground force plate. Repeated-measures correlations and linear mixed models were used to assess concurrent validity of accelerometer and force plate outcomes across wear sites. Results: Strong repeated-measures associations were observed between peak hip resultant acceleration and resultant LR (r rm 1169 = 0.74, P < 0.001, 95% confidence interval = 0.718, 0.769) and peak hip resultant accelerations and resultant GRF (r rm 1169 = 0.69, P < 0.001, 95% confidence interval = 0.660, 0.720) when data were combined across activities. By contrast, small to moderate associations were seen between ankle-based outcomes and corresponding GRF and LR during walking and jogging (r rm 209 = 0.17-0.34, all P < 0.001). No significant associations were seen with wrist-based outcomes during any activity. In addition, linear mixed models suggested that 24%-50% of the variability in peak GRF and LR could be attributed to measured accelerations at the hip. Conclusion: Peak accelerations measured at the hip were identified as the strongest proxies for skeletal loading assessed via force plate.

The external focus and internal focus effects on motor performance and skill acquisition have been extensively examined and reviewed in laboratory research. However, the use of attentional focus in the field has not been summarized. Therefore, the present study conducted a systematic review of literature regarding the use of external/internal focus by practitioners (therapists and coaches) and recipients (patients and athletes). From 1999 to 2020, twelve studies examined how external/internal focus were used in the field. Results showed both therapists and coaches predominantly used internal focus; athletes tended to use more internal focus but varied by sports; and attentional focus varied between practice and competition. Additionally, the present review also consistently found that external/internal focus accounted for a small proportion relative to other foci outside the external/internal focus paradigm. Importantly, the differences in results were largely dependent upon the type of assessment ( e.g. closed-ended and open-ended questionnaires). Future research needs to investigate the relative importance of external/internal focus as opposed to other foci, as well as that affect a shift of attentional focus from one type to another.

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