EMG ACTIVITIES OF MONOARTICULAR AND BIARTICULAR MUSCLES DURING GOAL-DIRECTED BALLISTIC MOVEMENT

Eight subjects, who were seated with the upper arm supported in a hori zontal position, performed a series of elbow flexion and extension mov ements in which a visual target was provided together with an elbow an gle signal by vertically moving horizontal lines on an oscilloscope. F ive loading conditions were employed, which differed in the number of steel plates attached to the subject's wrist: 0, 0.65, 1.30, 1.95 and 2.60 kg. The electromyographic (EMG) activity of the bi-articular bice ps brachii (BB) was compared with the mono-articular brachioradialis ( BR) for each of three EMG components; the first and the second agonist burst (AG1, AG2) during flexion movements, and the antagonist burst ( ANT) during extension movements. The magnitude relations for each EMG component between the two muscles were evaluated by the BR/BB ratio. T he results showed that there were significant differences (p < 0.05) a mong the three EMG components in all but the no-loading condition. Fur ther a post-hoc test revealed that there were significant BR/BB differ ences (p < 0.05) between AG1 vs. AG2 in 0.65 and 1.3 kg loading condit ions and between AG1 vs. ANT in all but the no-loading condition. Thes e results may suggest that different neural processes underlie the act ivation of mono- and bi-articular muscles in the organization and the control of movements.