The brachialis is a muscle located in the upper arm, beneath the biceps brachii. It plays a crucial role in elbow flexion, allowing the arm to bend. The brachialis is primarily responsible for this movement, especially when the forearm is in a pronated position, meaning the palm is facing down. Originating from the lower half of the humerus, the brachialis inserts into the ulna, one of the forearm bones. This muscle is essential for various daily activities that involve lifting or pulling, making it important for overall arm strength and functionality.