Eden Gee1, Austin Nguyen1, Pratham Shah2, Harshvardhan Singh1. 1University of Alabama at Birmingham, Birmingham, AL. 2University of Alabama at Birmingham, Dothan, AL.

BACKGROUND: Jump training improves bone health, body composition, postural stability, balance, muscle strength, and muscle power in children and adolescents. Children with increased adiposity show lower net jump power, the exact biomechanical mechanisms of which are still unknown. Transition time, which is the time between eccentric-to-concentric phase during a jump, plays a critical role in utilizing the stored eccentric torque toward a greater concentric output resulting in greater jump height (JHt). It is unknown if adiposity affects lower extremity joint-specific transition time for different types of jump. Further, we do not know if adiposity affects jump height for different types of jump. Such information can provide insight into the mechanistic factors explaining jump performance in children with adiposity. Thus, we examined the relationship of jump height (JHt) for different types of jump with lower extremity joint-specific transition times and % total body fat. METHODS: We used a rigid body model, using 36 reflective markers, and floor-embedded force plates to collect jump data for countermovement (CMJ; jump preceded by a quick countermovement) and drop (DJ; jump off of a 0.015 m raised platform) jump in typically developing children (N = 20; age = 8 - 14 years). After familiarization, participants performed 3 trials of CMJ and DJ. JHt was calculated from the greater trochanter marker data. Transition time was calculated as the time period between the last data point of negative (eccentric) acceleration to the first data point of positive (concentric) acceleration. RESULTS: Transition time at the ankle was negatively related to CMJ JHt (r = -0.454; p = 0.045) while transition time at the hip tended to be negatively related to DJ JHt (r = -0.453; p = 0.052). % total fat was positively related to transition time at the ankle(rspearman = 0.469; p = 0.037) and hip(rspearman = 0.488; p = 0.034) for CMJ and DJ, respectively. % total fat was negatively related to CMJ JHt (rspearman = -0.498; p = 0.007) and DJ JHt (rspearman = -0.672; p = 0.002). CONCLUSIONS: Joint-specific greater transition time associated with adiposity, in part, explains lower JHt during CMJ and DJ.

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