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Abstract:

BACKGROUND AND AIM: The purpose of this study was to investigate postural adjustments that are made in response to raising the arm in one-handed ball catching, given that postural balance might be decisive for successful catching performance [1]. Specifically, it was examined if postural adjustments are a response to overcome the disturbance of balance or merely a consequence of the movement at hand. METHODS: Full body kinematics, kinetics and postural muscle activity while raising the arm when catching a fast-moving ball were compared to a well-studied reaction-time arm raising task. RESULTS: The focal movement of arm raising showed more elbow flexion in catching compared to the reaction-time task (Wilcoxon test, p<0.05). Consequently, smaller inertial forces for catching resulted in different postural control mechanisms. In catching, postural adjustments were initiated by co-activation of postural muscles for initial segment stabilization (Fig. 1, left panel), followed by an inverted pendulum mechanism for equilibrium control. Raising the arm in the reaction-time task resulted in early reciprocal muscle activity (Fig. 1, right panel) and segmental counter-rotating at hip-level in addition to the inverted pendulum mechanism to maintain balance. CONCLUSIONS: During arm raising for a reaction-time task or for unconstrained catching, anticipatory postural adjustments seem to be a consequence of the inertia of the movement itself (movement support), rather than a mechanism to overcome possible future disequilibrium [2,3]. Afterwards, compensatory postural mechanisms involving inverted pendulum control with additional segmental counter-rotation to maintain balance are suggested for raising the arm in a reaction-time task, while mainly an inverted pendulum mechanism accommodates equilibrium control when raising the arm for catching [4]. REFERENCES 1. Davids et al. Res Q Exerc Sport. 71: 69-73, 2000 2. Pozzo et al. Biol Cybern. 85: 39-49, 2001 3. Patla et al. Exp Brain Res. 143: 318-327, 2002 4. Hof. J Biomech. 40: 451-457, 2007