The effects of required amplitude and practice on frequency stability and efficiency in a cyclical task.

From an ecological point of view, motor learning emerges from the interplay of constraints on action, which shape behaviour towards the optimal solution, and practice, conceived as an active exploration of the work-space, to search this optimal solution. In the experiment reported here, we studied this interplay for a cyclical task performed on a ski-simulator. Our aim was to assess the respective effects of amplitude and practice on frequency variability and efficiency. On the basis of previous empirical findings, amplitude was expected, beyond a critical value, to constrain and stabilize the frequency of the movement. Three groups of participants practised during four sessions at three different amplitudes (15, 22.5 and 30 cm). The results showed that participants moving at large amplitude displayed more stable and more consistent frequencies. Nevertheless, there was no interaction effect between target amplitude and practice. On the other hand, movement economy and harmonicity increased with practice, but were not affected by amplitude. Finally, the results of transfer tests showed that the effects of large amplitude on frequency variability were not resistant to a subsequent decrease in target amplitude. These results suggest that constraints and practice act independently on motor behaviour, and that a high constraint could be detrimental to the development of effective search strategies.