Effects of long-term practice on coordination between different joint motions in street dancers

This study investigated practice-induced change in coordination among the movement of different joints in street dancers. It did so by quantifying similarities in shape and phase lag among hip, knee, and ankle joint angles. Skilled street dancers and non-dancers were asked to synchronize a standing position knee-bending movement to a metronome beat over a wide range of beat frequencies. The similarity in the shape between the time series of the joint angle pairs was characterized by the peak value of a cross correlation function (CCF). The peak value of CCF in the hip-ankle angle pair was found to be significantly greater in dancers than in non-dancers, indicating coordination to be higher in dancers. The phase lag between hip and knee/ankle joint movements characterized by the time shift of the peak CCF value was found to be significantly greater in dancers than in nondancers. Because humans intrinsically have difficulties in developing a phase lag among joint movements, the greater extent of coordination and larger phase lag in dancers suggests that motor learning of coordination among joint movements in street dance is characterized by a stabilizing coordination pattern that involves an increase in phase lag among joint movements. This stabilizing pattern may play an important role in artistic expressions in street dance.