Coordination patterns in ball bouncing as a function of skill

By observing the coordination patterns of people of different ages and skill levels bouncing a ball, the authors addressed hypotheses regarding (a) the relative increase and decrease of degrees of freedom with learning and (b) the order of progression in the changing organization of those degrees of freedom with development and learning. The movement patterns of the dominant arm and hand of subjects at various skill levels were contrasted in a cross-sectional design so that the way movement organization changes as a function of practice could be examined. Nine subjects aged between 4 and 22 years bounced a basketball at a preferred rhythm while standing still. Each performance trial was videotaped, and motions of arm and ball were digitized. Statistical analyses were made of linear and angular body motions: pairwise correlations and multiple regressions, amplitude and period variability, phase relations, and spectral and coherency measures. The coordination patterns revealed that (a) the movement patterns of less skilled subjects were more variable than those of more skilled subjects and (b) the motions of the articulators showed directional changes as a function of skill level that began both proximally and distally and moved toward the center of the effector chain with practice. The findings point up the relevance of studying change of system organization for understanding control and coordination.