Adjustment to change in familiar and unfamiliar task constraints.

The aim of this study was to assess the rate of adjustment to changes in task constraints that are familiar and unfamiliar when a change in the pattern of sequencing of segmental movements is not required. The selected task was underwater flutter kicking with flippers (familiar) and without flippers (unfamiliar). Nine male competitive age-group swimmers were assigned either to an unfamiliar "leg flipper" task, a familiar "foot flipper" task or a "control" group to perform five trials without flippers (all groups), 60 trials with flippers, and a post-test comprising 10 trials without flippers (all groups). Kinematic variables were calculated from digitized video data. Whether the movement pattern was appropriate for the task was indicated by the percent power in the fundamental Fourier frequency harmonic of the vertical oscillations of the hip, knee, and ankle, and by a "velocity index" that was defined as the ratio of the hip-to-knee and knee-to-ankle velocities of the fundamental Fourier waveform. Adjustment to reproduce the appropriate movement pattern occurred within the first block of 10 trials regardless of whether the constraints were familiar or unfamiliar. However, optimal performance in terms of swimming speed was not obtained following change to the unfamiliar constraint until after 10 trials.