Medial HeadMedial Head of Triceps Brachii

armsCaput mediale musculi tricipitis brachii

The medial head of the triceps lies underneath the other two, against the arm bone. It is the workhorse of elbow extension, working at every load rather than only heavy ones.

Medial Head highlighted on an anatomical figure, from the front.
Where it sits, from the front.

The medial head lies deepest, directly against the back of the upper arm bone and mostly covered by the long and lateral heads. Only a small strip of it is visible near the elbow, on the inner side of the arm just above the joint.

It is the head that works all the time. Where the lateral head contributes more as resistance rises and the long head's contribution depends on shoulder position, the medial head is active from the lightest elbow extension upward and through the whole range. Some descriptions call it the prime mover of elbow extension for this reason, with the other two as reinforcements.

Like the lateral head it crosses only the elbow, so its length is unaffected by what the shoulder is doing.

It sometimes gets described in training material as the head trained by a particular grip or a particular angle. There is no good basis for that: it is working in every elbow extension regardless.

Training notes

Any triceps work trains it, which is the honest answer. It gets no benefit from being singled out because there is no position in which it is not already contributing.

It is the head most involved in light, high-repetition extension work, since it is active from the lowest loads. Rope pushdowns and band extensions load it thoroughly.

Its practical contribution is to the thickness of the arm just above the elbow rather than to the outline higher up, which belongs to the lateral and long heads.

Anatomy

Origin
  • Posterior surface of the humerus, below and medial to the radial groove
Insertion
  • Olecranon of the ulna, through the common triceps tendon
Actions
  • Extends the elbow, active through the whole range and at every load
Innervation
Radial nerve (C6–C8)

Exercises

Antagonists

Synergists