The effects of practice on limb kinematics in a throwing task.

The effect of practice on limb kinematics in a dart-throwing task was examined to test three current hypotheses regarding limb control: trajectory formation; end-point control; and coordinated joint-space control. Practice was given to both the relatively well-practiced dominant ant the relatively unpracticed nondominant limbs of 5 male subjects to permit analysis of the early phase of coordination acquisition. The nondominant limb demonstrated high absolute joint cross-correlations with high variability throughout practice and consistency in the hand trajectory. The dominant limb exhibit a significant decrease in wrist-elbow and wrist-shoulder cross-correlations over practice while also maintaining a consistent hand trajectory and significantly higher scoring performance. The findings demonstrate that practice effects can be seen in both coordination mode and variability of various parameters of limb motion, but the changing relationship between the variables suggests that control cannot be ascribed to any one of the three hypotheses advanced. It is proposed that the observed invariance or variance in limb trajectories, end-point control, and coordinated joint angles are a reflection of more global parameters emerging from the flow field properties of the organism, environment, and task interaction.