Muscle activity patterns during quick change of movement amplitude in rapid elbow flexions

ln this study, we investigated control of muscle activity for changing the amplitude of movement in rapid flexions at the elbow joint. This study focused on the changes in a triphasic electromyographic(EMG) pattern, i.e., the first agonist burst(AG1), the second agonist burst (AG2) and the antagonist burst (ANT), for increasing the amplitude of movement requires after the initiation of movement. Subjects performed 40 degree (Basic task) and 80 degree of flexion (Wide task). These tasks were performed under two conditions; performing a predetermined task (SF condition) and performing a task in response to a visual stimulus immediately after movement commencement (ST condition). Kinematic parameters (movement amplitude, movement velocity and movement time) and EMG activity (onset latency, duration and average EMG) from the agonist(biceps brachii) and the antagonist(triceps brachii) muscles were recorded. As a result, in both tasks, the onset latency of AG1, ANT and AG2 in the ST condition increased compared with those in the SF condition. In addition, the duration of ANT and AG2 and the a-EMG of AG2 increased in the ST condition. It is concluded that the control of muscle activity for changing the amplitude of movement in the ongoing movement was to control the onset and duration of ANT for changing the timing of stop movement and the duration and amplitude of AG2 for stopping the desired position accurately