Fist clenching movement. Artwork of the muscles of the forearm and hand from the front, with red arrows showing the direction of movement of the fingers during flexion to form a fist. Finger flexion is controlled by the flexor digitorum superficialis, flexor digitorum profundus, and lumbrical muscles. Here, the thumb folds under the fingers. The nerve used is the ulnar nerve. This is the left hand. For the right hand, see C016/6795.