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The biceps brachii is a muscle located in the upper arm that flexes the elbow joint and rotates the forearm so the palm of the hand turns face-up, an action known as supination. It originates on the top of the shoulder blade, runs along the front of the upper arm, and inserts at the radius bone in the forearm just below the elbow. A Latin term meaning “two-headed muscle of the arm,” biceps brachii refers to the muscle’s defining physical characteristic: Two separate sections, or heads, that originate at separate points on the shoulder blade and converge into a single tendon that crosses the elbow joint.
Commonly referred to as simply “the biceps,” the biceps brachii is primarily responsible for rotating the forearm when the elbow is flexed; when the arm is straight the supinator muscle of the forearm rotates the palm up. It plays an additional role in flexing the elbow, in which it assists the brachialis muscle, which lies beneath the biceps, and it is also involved in flexing the shoulder joint. As such, the biceps brachii performs actions at three arm joints: The proximal, or upper, radioulnar joint, the humeroulnar or elbow joint, and the glenohumeral or shoulder joint.
There are two types of strength-training exercises recommended for strengthening and adding size to the biceps muscle — compound exercises and isolated exercises. Compound exercises involve multiple muscles and joints, and those that work the biceps brachii include the chin-up, dumbbell rows and barbell rows, and the inverted or bodyweight row. In all of these exercises, the biceps act as a secondary muscle to the muscles of the upper back, but because each exercise requires flexing the elbow joint, the biceps can be more or less involved depending on the type of grip used.
The best known isolated biceps exercise, isolated in that it focuses on a single muscle group, is the biceps curl. This exercise can be performed using dumbbells or a barbell, but fitness experts mostly recommend the dumbbell curl because it allows for rotation of the forearm. It is also recommended to either alternate arms or simply curl one arm at a time, as it minimizes the risk of using the low back to help lift the weights.
To perform the dumbbell curl, one should stand with a dumbbell in each hand and grip neutral, or palms facing inward. He should then begin to curl the weight toward the shoulder, supinating the forearm as the elbow bends so that the palm faces inward and making sure to hold the upper arm tight to the body. Once the elbow is fully flexed, he should slowly lower the weight back to the starting position without swinging the dumbbell or allowing for momentum from gravity. Recommendations for sets, repetitions, and rest periods can vary depending on the desired result, so anyone training the biceps brachii should contact a fitness professional for more information.