Long HeadLong Head of Biceps Brachii

armsCaput longum musculi bicipitis brachii

The long head of the biceps starts inside the shoulder joint itself and runs down the outside of the upper arm. It is the outer half of the biceps and the part that forms the peak.

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

The long head has the most unusual route of any muscle in the arm. It starts on a small bump just above the shoulder socket, inside the joint capsule, then its tendon arcs over the top of the ball of the shoulder and drops into a groove on the front of the arm bone before becoming muscle. It is the only tendon in the body that runs through a joint on its way somewhere else.

Below that it forms the outer half of the biceps — the side nearest the shoulder when your arm hangs. This is the part responsible for what people call the biceps peak, the height of the muscle when the elbow is bent and the arm is flexed.

Because it crosses the shoulder further from the joint's centre than the short head does, it is the head most affected by where the elbow is. With the arm behind the body the long head is stretched; with the elbow raised in front, it is already shortened and has less left to give.

It also helps hold the ball of the shoulder in its socket, in the same way the rotator cuff does. That is a secondary role and a contested one — how much the long head contributes to shoulder stability is genuinely argued about — but it is why the tendon comes up so often in discussions of shoulder problems.

Training notes

Curls done with the elbows behind the torso emphasise it. An incline dumbbell curl, lying back so the arms hang behind the body, puts the long head at its longest and makes the bottom of the range the hard part. That is the closest thing to a long-head-specific movement.

The reverse applies to preacher curls, where the elbows sit forward on a pad: the long head is already shortened at the shoulder, so the short head and the brachialis take more of the work.

The peak is largely a matter of where your long head's belly sits along the arm and how long its tendons are, and no exercise changes either. Training makes the muscle bigger; it does not move it.

Anatomy

Origin
  • Supraglenoid tubercle of the scapula
Insertion
  • Radial tuberosity, through the shared biceps tendon
Actions
  • Supinates the forearm
  • Flexes the elbow
  • Assists flexion and abduction of the arm, and helps hold the head of the humerus in the socket
Innervation
Musculocutaneous nerve (C5–C6)

Exercises

Antagonists

Synergists