Practice effects on decreasing and increasing force-control during periodic isometric movements of the index finger.

The present study examined whether improvement in control while decreasing force to achieve a lower force target would be facilitated by comparison of performance while increasing force to achieve a higher force target. Participants practiced control of isometric force and timing during a unimanual force production task cycling between 5 and 10% of maximum voluntary contraction with a target interval of 500 msec. Although errors and variability of both peak and valley forces and interval decreased during early practice, the valley force was still more inaccurate and variable than the peak force in the final practice. Variabilities of both forces did not decrease when the valley force was synchronized with an audible metronome pulse but did decrease when the peak force was synchronized with it.