Final answer:
The brachialis muscle performs the same action as the biceps brachii and brachioradialis, which is flexing the forearm.
Step-by-step explanation:
The brachialis muscle has the same actions as the biceps brachii and the brachioradialis. These muscles work in flexing the forearm. The biceps brachii is a two-headed muscle that is involved in flexing the forearm at the elbow, aiding in supinating the forearm at the radioulnar joints, and flexing the arm at the shoulder joint. Similarly, located deep to the biceps brachii, the brachialis muscle provides significant power during forearm flexion. The brachioradialis muscle, on the other hand, is adept at flexing the forearm quickly and assisting in lifting loads slowly.