The tricep brachii is a single muscular unit with three distinct heads: the medial, the lateral and long heads. It functions as a powerful extensor of the upper extremity. Each head has a different fatigue rate and each head becomes more or less active relative to shoulder elevation.
At 0 degrees of elevation the long head of the triceps applies the most muscle force. As the shoulder becomes more elevated, reaching 90 degrees and higher the medial head of the triceps becomes the dominant extensor.
Training Tricep Push-down on the Pendulum Rack System
