Abstract
[Purpose] This study examines the effect of isometric contraction of the upper limb on the affected side in the supine position on the activity of body trunk muscles on the opposite side of normal adults. [Participants and Methods] The research participants included 10 normal adults. A handheld dynamometer device was used to measure the isometric contraction of the upper limb. The muscle activity of the body trunk was analyzed by electromyography. [Results] The muscle activities of rectus abdominis, internal oblique abdominis, erector spinae muscle, and multifidus muscle of the body trunk on the opposite side were significantly larger in the case of the adduction and flexion of the shoulder joint on the affected side than in the case of abduction and extension. [Conclusion] The isometric contraction induced by the adduction and flexion of the shoulder joint on the affected side altered the muscle activity of the body trunk on the opposite side.