The purpose of this study was to assess the effect of bed rest on appendicular muscle torque. Fifteen healthy male volunteers between the ages of 21 and 54 participated in the study. The subjects were put on five weeks of strict horizontal bed rest. They were allowed to sit up for bowel movements only; however, no lower extremity weight-bearing was allowed. During bed rest, the subjects were required to ingest a fixed nutritionally adequate diet. Data for muscle torque were obtained using a Cybex II dynamometer, Upper Body Exercise Table (UBXT), and a data analysis computer (HUMAC). The subjects were tested on Cybex at the speed of 60 degrees/sec during the week before starting bed rest and the day after starting reambulation. The muscle groups tested were soleus, gastrocnemius-soleus, dorsiflexors, knee flexors, knee extensors, elbow flexors, and elbow extensors. The torque in all groups but elbow extensors was reduced by 24%, 26%, 8%, 8%, 19%, and 7%, respectively. Student's t-test for paired means demonstrated significant loss of torque in all muscle groups except elbow extensors (p less than 0.05). The results of this study suggest that a strengthening exercise program should be administered to these patients while they are on bed rest, and that the earliest possible attempt should be made to ambulate patients after prolonged bed rest to minimize the loss of muscle torque.