EFFECTS OF VARYING FORCE COMPONENTS ON EMG REACTION-TIMES OF ISOMETRIC ANKLE DORSIFLEXION

The effect of variation in contraction force is one of the most important factors in the organization and execution of voluntary movements. However, there have been discrepancies between previously reported results and their underlying assumptions. Thus, the present experiment was designed to test whether varying the amount of force required to perform an isometric movement influenced simple reaction time (EMG-RT). Subjects were asked to respond in accordance with (T+) or without a visual target (T-) under the conditions of varying contraction forces. The results showed that the EMG-RTs decreased with an increase in contraction forces under the T+ condition but there were no significantly different EMG-RTs under the T- condition in spite of obviously different contraction forces. Under the T- condition there was no significantly different correlation coefficient between the peak values of dF/dt and EMG-RTs. However, under the T+ condition the correlation coefficient was negative and statistically significant. Those results indicated that the EMG-RT was not affected by an increase of the magnitude of force required to execute the movement, but by the time manipulation. Therefore, movements which were to be performed slower were associated with a significant increase in EMG-RT. © 1990.