Biceps Anatomy: Muscles and Function

More than one muscle

Say "arm muscles" and most people immediately think of the biceps and triceps — which is broadly correct, but the reality on the front of the upper arm is a bit more layered than that.

The biceps

What we casually call "the biceps" is actually made up of three separate muscles:

• biceps brachii
• coracobrachialis
• brachialis

All three act as flexors of the elbow joint, and they also assist with certain movements at the shoulder.

The largest of the three is the biceps brachii, which, as its name suggests, has two heads — a long head that originates from a tendon at the shoulder joint, and a short head. The two heads join into a single muscle belly before ending in a tendon that attaches to the radius. The biceps brachii is worked during forearm flexion (the classic barbell curl, for example) and during certain shoulder movements — lateral raises, front raises, and rear raises. It's also the most visible muscle on the front of the upper arm, which is exactly why it gets the lion's share of arm exercises.

The coracobrachialis is an interesting case: despite sitting on the front of the arm, it isn't really worked by standard biceps exercises. That comes down to where it attaches — it originates on the shoulder blade and inserts around the midpoint of the humerus. The coracobrachialis assists in bringing the arm in toward the body and in raising it forward.

The last muscle we'll cover today is the brachialis. It sits underneath the biceps brachii (with its insertion on the upper part of the ulna), and if you want to target it more directly, hammer curls are the exercise of choice.

In the next installment of this anatomy series, we'll take a look at the triceps.