Resistance bands for chin-ups are a great way to build strength for bodyweight chin-ups. The main muscle this exercise targets is the latissimus dorsi. Moreover, muscles that act as a synergist to assist the lats during chin-ups are the biceps brachii, brachioradialis, brachialis, triceps, infraspinatus, teres minor, teres major, lower trapezius, pectoralis major, external abdominal oblique, and erector spinae.