Motor variability regulation analysis in trampolinists.

In trampolining, optimizing body orientation during landing reduces injury risk and enhances performance. As trampolinists are subject to motor variability, anticipatory inflight corrections are necessary to regulate their body orientation before landing. We investigated the evolution of a) body orientation and b) limb position (i.e., arms and legs) variabilities. Secondary objectives were to investigate c) the link between acrobatics difficulty and the variability accumulation, and d) to identify links between body orientation variability and gaze orientation. Kinematics and gaze orientation were captured using inertial measurement units and an eye tracker, respectively. Seventeen trampolinists performed up to 13 different acrobatics (different number of rotations in twist and somersault). Intra-trampolinist pelvis orientation and limb position inter-trial variability was computed for each acrobatic at three key timestamps: takeoff, 75 % completion of the twist, and landing. Pelvis orientation variability significantly increased between takeoff and the instant when 75 % of the twist is completed (+75 %) and then decreased from the instant when 75 % of the twist is completed until landing (-39 %). Conversely, limb variability decreased (upper limbs: -66 % and lower limbs: -46 %), before increasing (+357 % and +127 %), suggesting that trampolinists adapted their limb kinematics to regulate pelvis orientation before landing. It was qualitatively observed that this decrease in body orientation variability occurred mostly when trampolinists were looking at the trampoline bed before landing. In addition, there was a moderate correlation between the number of twists in a straight somersault and the variability accumulation at 75 % of the twist, highlighting that trampolinists accumulate more variability as the number of twist rotations increases.