Coordination changes in a discrete multi-articular action as a function of practice.

This study investigated how novices re-organized motor system degrees of freedom when practicing a multi-articular discrete kicking task. Four male participants practiced a soccer chipping task to seven different target positions over 12 sessions for 4 weeks. Data from each participant indicated changes in degrees of freedom involvement as a function of practice. Further, each participant showed a different progression of change in levels of joint involvement for hip, knee and ankle in the kicking limb. Cross-correlations between joints in the kicking limb also showed different pathways of coupling and de-coupling with practice. Performance outcome scores improved and variability of intra-limb coordination decreased as a consequence of practice for all participants. Angle-angle plots also showed qualitative changes in intra-limb coordination between early and late practice sessions. Evidence suggested that foot velocity at ball contact was functionally manipulated by participants when kicking to target positions with varying height and distance constraints. Referencing data to a model of learning [Newell, K. M. (1985). Coordination, control and skill. In: Goodman, D., Franks, I., & Wilberg, R.B. (Eds.), Differing perspectives in motor learning, memory, and control. Amsterdam: North-Holland, pp. 295-317] determined that progression through different stages of learning may not be sequential and could alternate between learning stages. The present study highlighted individual differences in acquisition of coordination and control of joint motion even under similar task constraints, showing how degeneracy in movement systems facilitates learning.