The biceps brachii is one of the most frequently trained muscles, located on the front of the upper arm and shaped like a spindle. The biceps brachii has two heads, hence the name "biceps": the long head and the short head. It is part of the skeletal muscle system and falls under the category of limb muscles. Typically, most people desire larger biceps, and this desire is often justified. The primary function of the biceps brachii is known to be elbow flexion, which occurs during bending movements. However, its duties extend beyond just curling motions. Composed of the long and short heads, it's referred to as the biceps. Both heads originate from the scapula and insert into the radius.

Short Head

The short head of the biceps is responsible for the curling motion. Additionally, the short head is involved in supination of the forearm, which is the twisting of the forearm until your palm faces upwards. It also assists in shoulder flexion (lifting the arm straight forward), horizontal adduction (when your arm is extended directly to your side, and you move your arm forward), and adduction of the shoulder (when your arm is extended out to your side and then pulled toward your torso).

Long Head

The long head of the biceps shares some functions with the short head, including elbow flexion, forearm supination, and shoulder flexion. The long head also aids in shoulder abduction, which occurs when you lift your arm to the side. The long head only assists in shoulder abduction when the shoulder joint is externally rotated.

Due to the different origins and paths of the long and short heads, curling movements that involve shoulder flexion (when the arms are in front of you or above) tend to preferentially engage the long head.