There is growing empirical evidence lending support to the existence of an “upper body strategy” to extend the ankle and hip strategies in maintaining upright postural stability among adults. Both postural stability and arm movement functions are still developing in children. Therefore, enquiry concerning arm contribution to postural stability among children is needed. This proof of concept study seeks to determine whether the arms play a functionally relevant role in dynamic postural control among children. Twenty-nine children (girls, n = 15; age, 10.6 ± 0.5 years; height, 1.48 ± 0.08 m; mass, 42.8 ± 11.4 kg; BMI, 19.2 ± 3.7 kg/m2) completed three dynamic balance tests; (1) Y Balance test®, (2) timed balance beam walking test, (3) transition from dynamic to static balance using the dynamic postural stability index (DPSI). Each test was performed with free and restricted arm movement. Restricting arm movements elicited a marked degradation in the Y Balance reach distance (all directions, P ≤ 0.001, d = -0.85 to -1.13) and timed balance beam walking test (P ≤ 0.001, d = 1.01), while the DPSI was the only metric that was not different between free and restricted arm movements (P = 0.335, d = -0.08). This study provides direct evidence that the arms play a functionally relevant role in dynamic balance performance among children. These findings may provide the impetus to develop training interventions to improve the use of the arms in activities of daily living.

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This document is the author's post-print version, incorporating any revisions agreed during the peer-review process. Some differences between the published version and this version may remain and you are advised to consult the published version if you wish to cite from it.

Background: Sprint running is a key determinant of player performance in soccer that is typically assessed and monitored using temporal methods. Purpose: The aim of this study was to examine the relationship between ground reaction force kinetics at the first step and sprint running performance in soccer players in order to enhance the development of training and assessment methods. Methods: Nineteen semiprofessional soccer players participated (mean ± s: age 21.1 ± 1.9 years, body mass 79.4 ± 7.3 kg and stature 1.79 ± 0.06 m). The participants completed 20 m acceleration sprint runs as timing gates recorded split times between 0-5 m, 5-10 m, 10-15 m, 15-20 m and 0-20 m. A force plate captured vertical, anteroposterior and mediolateral ground reaction force data (1000 Hz) of the first right foot strike stance phase. Results: Ground reaction force metrics, including peak anteroposterior propulsive force (r =0.66 to 0.751; P =0.000 to 0.002), peak vertical ground reaction force (r =0.456 to 0.464; P =0.045 to 0.05), average medial-lateral/anteroposterior orientation angle (r =-0.463; P =0.023), and average anteroposterior/vertical orientation angle (r =-0.44; P =0.03) were correlated with one or all split times between 0-5 m, 5-10 m, 10-15 m, 15-20 m and 0-20 m. Conclusions: Acceleration sprint running in soccer requires minimised mediolateral and increased anteroposterior loading in the stance phase. Multicomponent ground reaction force measures of the first step in acceleration sprint runs are important for developing performance assessments, and understanding force application techniques employed by soccer players.

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