Although the biceps get all the spotlights, there are four major upper arm elbow flexor muscles: the biceps brachii, the brachialis, the brachioradialis and the teres pronator. The brachialis is the muscle under the biceps that contributes to elbow flexor size. If your pronated curling strength is not 82% of your supinated grip strength, your brachialis is weak and most likely under-developed. You can’t escape it, want big arms?
