RELATIVE CONTRIBUTIONS TO THE NET JOINT MOMENT FOR A PLANAR MULTIJOINT THROWING SKILL - EARLY AND LATE IN PRACTICE

The purpose of this investigation was to determine for a planar multij oint throwing skill, if the relative contributions of the components o f the net joint moment (NJM) at the elbow and shoulder change after pr actice. Each participant (N = 7) performed 200 throwing trials equally distributed across 5 consecutive days. Each participant threw a 0.15- kg ball as far as possible using the nondominant arm while the motion of the throwing arm was restrained to a horizontal plane. From video d ata and body segment inertial estimations, NJMs and NJM components (i. e., generalized muscle moments and motion-dependent moments) were calc ulated for selected early and late practice trials Performance (throwi ng distance) showed an expected improvement from early to late practic e. The dynamics analysis indicated that participants increased average NJMs and NJM components at both joints. However; the relative contrib ution of NJM components, expressed as ratios of those components to th e NJM at each joint, did not change after extended practice. Restraini ng the throwing arm to a horizontal plane may partly explain why no ch anges were found in the relative contributions of NJM components. The lack of change in moment ratios support a motor strategy of scaling jo int moments for faster movements.