The triceps brachii is a large three-headed muscle located on the back of the upper arm. The tricep is the primary extensor of the elbow consisting of the long, medial and lateral heads.
When exercising at 0 degrees elevation the long head of the triceps brachii produces higher muscle force and activation than the lateral and medial heads. There is no significant difference between the forces of the lateral and medial heads at this angle.
Once shoulder elevation reaches 90 degrees the medial head of the tricep produces significantly higher muscle force which continues while raising your arm to an overhead position. At 90 degrees there is no difference in force between the lateral and long head of the triceps. Raising your arm straight overhead is approximately an 185 degree movement and as the elevation approaches this angle the lateral head force begins to exceed the long heads.
Putting all this in terms for training — the long head of the tricep plays the main role of extending the elbow and as the shoulder angle elevation increases the medial head takes over. This is an important consideration for fully developing the triceps brachii when training to Get Strong.
Tricep Pressdown at Zero Degrees while training on the Pendulum Rack System
