The biceps curl is a highly recognizable weight-training exercise that works the muscles of the upper arm, and to a lesser extent, those of the lower arm. It's a great exercise for seeing results in strength and definition. Curls work the biceps muscles at the front of the upper arm, and also the muscles of the lower arm—the brachialis and brachioradialis. You use these muscles anytime you pick something up, which is common throughout daily life. Doing the standing arm curl,