Quantitative Time-Profiling of Children's Activity and Motion.

Introduction: The aim was to establish children's mechanical movement patterns during a standardised assessment of fitness by means of an accelerometer. Further to this, our objective was to use the information from the accelerometer to profile individual time courses of exercise, across the cohort. Methods: A multi-stage fitness test study was performed with 103 children, aged 10.3 years +/- 0.6y. Children wore an ankle mounted accelerometer and gait data was collected on radial acceleration traces obtained at a frequency of 40 Hz. Time resolved metrics of foot impact force, maximum leg lift angle and stride frequency were used to profile children's performance across the test duration. A whole-history metric of stride quality, based on the changing ratio of stride length to stride frequency, was used in bivariate analyses of physical performance and body metrics. Results: Stride angle derived by our protocol was found to have a strong positive correlation with integrated acceleration, synonymous with counts, widely used in the sport science community (r = 0.81, r = 0.79 and r= 0.80 across different stages of the multi-stage fitness test). Accelerometer data show that differing performance in the test is related to the children's ability to accurately control their gait, with high performers displaying a linearly increasing speed, delivered through stride extension and well matched to the demand level of the test. A negative correlation was found between stride quality and body measures of BMI (r = -0.61), body mass (r = -0.60). Conclusion: Profiles of the gait parameters provide information on the mechanics of child's motion, allowing detailed assessment of multiple parameter during increasing intensities of exercise. (C) 2016 American College of Sports Medicine

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