Bicep Curl

Biceps Brachii Muscle

Your biceps brachii muscle (long head) is attached to your shoulder blade (scapula) in two places. This twin configuration is reflected in the name biceps, meaning two heads. It follows down along your upper arm bone (humerus) and is inserted by a tendon on your lower arm bone (radius). When it contracts, your forearm is pulled up, with your arm bending at the elbow. Although this is the primary mover during biceps curls, it's far from the only muscle at work.

Brachialis and Brachioradialis

Your brachialis muscle sits under the biceps brachii. It's a long muscle that flexes your elbow. It connects your upper arm bone (humerus) to the long forearm bone (ulna). Your brachioradialis muscle assists the brachialis with flexing your elbow and connects your humerus bone to the short lower arm bone known as the radius.

Deltoid Muscle

Your deltoid muscle is the rounded muscle that curves around the outer part of your shoulder and upper arm. The muscle forms a triangle shape, with the wide part of the triangle attaching to your shoulder blade (scapula) and your collarbone (clavicle) before stretching down to your humerus bone. The deltoid is responsible for several motions; in this case, it helps bring your upper arm forward if you aren't strictly isolating the elbow joint during your biceps curls.

What Is Happening During a Bicep Curl?

The biceps curl is a fundamental exercise targeting the biceps muscles, the muscles on the front of your upper arm. No other muscles are directly involved in a biceps curl, although several muscles assist during the movement. During the curl exercise, the biceps muscle shortens then lengthens to control the movement of the weight.

The biceps curl can be done with a barbell, resistance band, dumbbells or a cable machine. Although the type of resistance changes, the movement is the same. The exercise starts with your arm straight down at your side, your palm facing forward. Bend your elbow to curl the weight up until your palm is almost touching your shoulder. Your upper arm should stay locked in place next to your side with your elbow pointing toward the floor.

A muscle contracts when the muscle fibers create tension against an external resistance. Your biceps muscle contracts both concentrically and eccentrically during the biceps curl. When you curl the weight up, the biceps muscle creates enough force to overcome the external resistance. During this phase of concentric contraction, the muscle fibers shorten, pulling at the elbow joint and lifting your forearm. When you lower the weight, the muscle fibers do not create enough force to overcome the external resistance. The fibers lengthen during this eccentric phase to control the descent of the weight.

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