Objective
This study was designed to investigate the effect of forearm position on the maximal isometric voluntary supination and pronation strengths and EMG activities in the related muscles.

Method
The maximal isometric supination and pronation strengths were measured in 14 normal male subjects using Work simulator^Ⱂ at 4 different forearm rotation position. EMG activities were simultaneously measured in supinator and biceps brachii during supination and pronator quadratus and pronator teres during pronation.

Results
The maximal isometric supination strength and EMG activities of biceps brachii and supinator were significantly higher as the forearm was more pronated (p＜0.05). The maximal isometric pronation strength and EMG activi-ties of pronator teres were significantly higher as the forearm was more supinated (p＜0.05). The maximal isometric supination and pronation strengths were higher in the dominant side than those of the nondominant side (p＜0.05) and EMG activities of pronator teres and supinator were higher in the dominant side than in the nondominant side (p＜0.05).

Conclusion
The supination and pronation strengths and EMG activities of related muscles were influenced by the forearm rotation position. Therefore the forearm position should be considered in evaluation of upper limb strength and function, and rehabilitation of upper extremity for improving strength and minimizing the overuse of supination and pronation. (J Korean Acad Rehab Med 2002; 26: 432-438)