Effects of wrist flexion and extension on forearm pronation force

Abstract

Effects of wrist flexion and extension on forearm pronation force were studied. The forces produced by maximal pronation (FMP) with the wrist relaxed (RP) , maximally flexed (FP) and maximally extended (EP) in the forearm 90° (supine), 60° (S60°), 30° (S30°), and 0° supinated (neutral) positions were measured in eight normal human subjects. The FMP of RP, FP, and EP were, respectively, 8.3±1.8 (mean±S.D.), 10.2±2.2, and 5.7±1.4 kg in the supine, 6.9±1.8, 8.0±2.3, and 4.8±1.4 kg in the S60°, 5.1±1.3, 4.8±1.3, and 3.3±1.0 kg in the S30°, and 3.5±0.8, 3.0±0.8, and 2.1±0.6 kg in the neutral position. The FMP of EP was small in every forearm position and the respective FMP of RP, FP, and EP decreased with changing the position from supine to neutral. Assuming the FMP of RP in each position as 100%, the FMP of FP was 124±7%, 116±8%, 95±23%, and 86±12%, and the FMP of EP was 68±10%, 71±17%, 64±14%, and 61±20%, respectively, in the supine, S60°, S30°, and neutral positions. The FMP of FP in the supine and S60° positions was larger and the FMP of EP in every position was smaller than RP. The results suggest that the force is reinforced by the flexion and weakened by the extension.