2011 Volume 9 Issue 2 Pages 65-69
Changes of forearm supination force by changing flexion angle of the elbow joint were studied in eight normal human subjects. The subject sat on a chair and put the upper arm and forearm on a table with the shoulder 90° abducted, 0° flexed, and 0° rotated and the forearm 0° pronated (neutral position). The force (kg) of maximal supination was measured while elbow angle was changed from the maximum extension (0°) to 130° flexion by 10° step. The force was 3.9±1.2 (mean±S.D.), 4.5±1.2, 5.1±1.1, 6.2±1.1, 6.8±0.9, 7.7±1.1, 8.5±1.2, 8.3±1.4, 7.7±1.3, 7.3±0.9, 6.5±1.6, 6.0±1.7, 5.4±1.5, and 4.8±1.2 kg, respectively, at 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90°, 100°, 110°, 120°, and 130° flexion. The force increased gradually from 0° to 60° flexion and then decreased very gradually from 70° to 130° flexion. The force at 60° flexion was 2.2 and 1.8 times as large as that at 0° and 130° flexion, respectively. Since m. biceps brachii is a strong supinator, the results of the present study should be caused by changes of the length of its muscle fibers and the angle of its distal tendon to the insertion with elbow flexion.
