Body Stabilization and the Strength of Arm Extension

Abstract

Nine subjects were measured to determine the maximum force of arm extension (push) at five elbow-angles at 25° intervals between 60° and 160°, and with five conditions of back support: no back support, and with a support at 20, 40, 60 and 80 per cent of the distance from the seat to the height of the shoulder joints. It was found that the strength of the response was influenced by the elbow-angle and the degree of body stabilization provided by the backrest. The backrest height had little effect at the lesser elbow-angles, but as the arm was further straightened to 135° or 160° the back support became an important factor in limiting the strength of the response. These results emphasize the importance of both joint angle and body stabilization in the production of usable muscle forces.