Chin-ups, like most pull-ups, target the latissimus dorsi muscle of the back as a shoulder extensor, scapular downward rotator and scapular depressor, in bringing the spine to the humerus. This is assisted by elbow flexors (brachialis, brachioradialis, biceps brachii) which bring the humerus to the forearm. Chin-ups, unlike pull-ups, also highly target the biceps. That is one of the main differences between pull-ups and chin-ups.