Isometric contraction of an upper extremity and its effects on the contralateral lower extremity.

[Purpose] The aim of this study was to examine effects of the isometric contraction of an upper limb in a supine position on the muscle activity of a healthy adult in the contralateral lower limb. [Subjects] The subjects were 40 healthy adults (35 males and 5 females). [Methods] The muscle activity of the rectus femoris (RF), biceps femoris, anterior tibialis, and medial gastrocnemius (MG) of the contralateral lower limb was measured using electromyography while the subjects flexed, extended, abducted, and adducted the shoulder joint of an upper limb. [Results] The muscle activity of the RF of the contralateral lower limb was significantly high when the subject flexed the shoulder joint of an upper limb, and the muscle activity of the MG of the contralateral lower limb was significantly high when the subject adducted the shoulder joint of an upper limb. [Conclusion] The isometric contraction that results from flexion and adduction of the shoulder joint of an upper limb in a supine position is considered to selectively affect the RF and MG activity of the contralateral lower limb.