Qualitative and quantitative change in the kinematics of learning a non-dominant overarm throw.

This study investigated changes in non-dominant overarm throw technique over practice from the perspective of three distinct though potentially complementary approaches to motor skill acquisition. Ten participants (mean ± SD age 22 ± 2 yrs, stature 1.71 ± 0.60 m, mass 73 ± 14 kg) completed 9-practice sessions (each 10 trials), during which whole-body kinematic data were collected. In line with the motor learning model of Newell (1985), we examined changes in the coupling between the centre-of-mass (CoM) and wrist motion. During initial practice, coupling was initially in-phase moving to wrist-led coupling with whole-body motion. With practice a more complex backwards wrist-led coupling that progressed to forward wrist-led coupling was observed. Secondly, in line with Bernstein's (1967) notion of freezing before freeing degrees of freedom; a significant increase in joint angle range of motion (ROM) at the lower limb joints and shoulder, and significant decrease in elbow and wrist ROM was observed. Thirdly, ROM changes coincided with the time course of changes in the four components of technique change in overarm throwing action proposed by Robertson and Halverson (1984). Participants began in mid to high action levels for the torso/arm components, while the step component progressed to higher action levels with practice. Common practice induced changes in the collective posture-ball release dynamics and were supported by individual strategies at the joint ROM level revealing the complementarity nature of the three approaches and their key dependent variables to the analysis of learning to throw.