The Ultimate Forearm and Bicep Guide: How to Curl for Complete Arm Size

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Modifying wrist rotation dramatically alters which muscle carries the burden of the lift. In a fully supinated grip, the tendon of the biceps wraps around the radius, giving the muscle optimal leverage to pull the bone upward. Turn the hand into a pronated grip, with palms facing down, and the biceps tendon wraps around the radius in a way that mechanically compromises its pulling angle.

With the biceps mechanically disadvantaged during pronation, the brachioradialis muscle steps in to execute the majority of the elbow flexion. Running along the lateral side of the forearm from the lower humerus to the base of the wrist, the brachioradialis possesses the longest lever arm of any elbow flexor. Neutral grips, such as those used during hammer curls, place the muscle in an intermediate position where both the brachialis and brachioradialis can produce exceptional force without being inhibited by forearm twisting.

Arm wrestling strength relies heavily on this exact structural configuration. Competitive arm wrestlers spend years developing the connection between the thumb-side wrist flexors, the pronator teres, and the brachioradialis to lock their arm angle under extreme counter-pressure. By rotating your wrists systematically throughout your training week, you manipulate these physiological leverage points to trigger comprehensive forearm hypertrophy.