The shoulder extension function of the triceps brachii.

The triceps brachii (TB), the sole muscle of the posterior humerus, acts an extensor of the elbow and shoulder. As a biarticular muscle, the angles of the elbow and shoulder influence its' ability to generate joint moments. The purpose of this study was to investigate the influence of elbow and shoulder joint angles on the shoulder extension function of the TB. Eighteen subjects were tested on a Biodex dynamometer with the TB selectively stimulated at a standardized level of voltage. The results revealed that the shoulder angle was the most important factor in the extension moment. As the shoulder angle moved from 0° to 80° the shoulder extension moment increased significantly. The increase in the shoulder extension moment between 0° and 80° was possibly due to the lengthening of the moment arm.