Effects of different types of mechanical load on the duration of the initial agonist pulse.

Ten right-hand-dominant subjects completed a series of unsighted, goal-directed, arm flexion movements under three different mechanical loading conditions: an inertial load, an elastic spring load, and a stretched-spring load. Subjects completed a series of inertial load training trials followed by random application of one of the three loads. Three time intervals of the first agonist pulse were considered for analysis: the time from initiation of agonist activity to the onset of movement, the interval from movement initiation to the end of the agonist pulse, and the duration of the entire agonist pulse. Analyses revealed that load type did not affect the duration of any of the time intervals studied. The results suggest the presence of a regulatory control process which temporally organizes an invariant agonist pulse even when the movement is perturbed by external loads possessing different mechanical characteristics.