Bi-articular muscles cross more than one joint and contribute to motion at both joints, and the extremities of the human body contain several such muscles. Actions produced by all muscles are determined, to a large extent, by joint moment arms and muscle length. These are transient factors which change as joint angles are altered. Measuring muscle moments while manipulating both joints will produce a better understanding of the actions of bi-articular muscles. This review summarizes investigations which have explored the actions of the biceps brachii as shoulder and elbow joints are moved into various angle combinations. Clinical implications of the findings are discussed.

The triceps brachii (TB) is the only muscle that lies along the posterior humerus, and its role in elbow extension has been the topic of investigation for many decades. The TB research has also included subjects such as strength training, effects of aging, training adaptions, etc. The purpose of this paper was to review some of the more unique investigations regarding the functions of the human TB. Specifically, this paper discusses articles that have explored the actions of the TB when manipulating the angles of the joints it crosses, the elbow and shoulder.

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