Electromyographic study of the elbow flexors and extensors in a motion of forearm pronation/supination while maintaining elbow flexion in humans

Activities of the elbow flexors (biceps brachii, BE; brachialis, B; brachio radialis, BR) and extensors (triceps brachii, TB) in a motion of forearm pr onation/supination with maintenance of elbow flexion (PS-movement) in nine healthy human subjects mere studied by electromyography (EMG). The subject performed the PS-movement slowly or quickly with or without a load extendin g the elbow. In the slow PS-movement, an increase and decrease of EMG activ ities during supination and pronation, respectively, mere seen in BE and th e reverse was in B. A clear increment of EMG activities in BE accompanied w ith a reduction of EMG activities in B and/or BR, and the reverse were ofte n observed. The contraction level and grain with the forearm supine mere hi gher and larger than those with the forearm prone, respectively, in BE and the reverse was in B and BR. In a series of the quick PS-movement, alternat ing increases of EMG: activities between BE and the other flexors (B and BR ) mere seen. Since TB showed no EMG activities throughout the experiment, i t is suggested that reciprocal contractions between BE and the other flexor s, which produce a complementary force in flexion direction, enable motions of pronation/supination with maintenance of flexion. Contraction propertie s of the flexors were discussed. (C) 1998 Tohoku University Medical Press.