Bicep Curls: Primary Joint Action, Anatomy, and Muscle Involvement

Which joint and joint action are correctly paired in order to perform bicep curls at the gym?

The primary joint action involved in performing bicep curls is elbow flexion, occurring at the elbow joint, where the forearm moves closer to the upper arm.

The Primary Movement: Elbow Flexion

In the context of resistance training, understanding the specific joint actions involved in an exercise is paramount for effective and safe execution. For the bicep curl, the fundamental movement is elbow flexion. This is an action in which the angle between the anterior (front) surfaces of the forearm and the upper arm decreases, effectively bringing the hand and forearm towards the shoulder. This movement occurs predominantly in the sagittal plane of motion.

Anatomy of the Bicep Curl: The Elbow Joint

The elbow joint is the primary articulation responsible for the bicep curl. It is classified as a hinge joint (specifically, a trochleoginglymus joint), which primarily allows for flexion and extension movements, much like a door hinge.

• Bones Involved: The elbow joint is formed by the articulation of three bones:
  • The humerus (upper arm bone).
  • The ulna (the larger forearm bone on the pinky finger side).
  • The radius (the smaller forearm bone on the thumb side).
• Articulations:
  • The humeroulnar joint (between the humerus and ulna) is the main hinge, facilitating flexion and extension.
  • The humeroradial joint (between the humerus and radius) also contributes to flexion and extension.
  • The proximal radioulnar joint (between the radius and ulna) allows for pronation and supination of the forearm, which can influence bicep activation (e.g., supinated grip for standard curls).

Key Muscles Involved in Elbow Flexion

While the bicep curl is named for the biceps brachii, several muscles work synergistically to produce elbow flexion:

• Biceps Brachii: This two-headed muscle is the most prominent elbow flexor, particularly effective when the forearm is supinated (palms up). It also assists in supinating the forearm.
• Brachialis: Often referred to as the "workhorse" of elbow flexion, the brachialis lies deep to the biceps brachii. It is solely responsible for elbow flexion, regardless of forearm position, making it a powerful and consistent contributor.
• Brachioradialis: This muscle is located in the forearm and contributes significantly to elbow flexion, especially when the forearm is in a neutral (hammer grip) or pronated (palms down) position.

These muscles act as agonists (prime movers) for elbow flexion, while muscles like the triceps brachii act as antagonists, opposing the movement.

The Role of Other Joints

While the elbow joint is the primary focus, other joints play crucial roles in stabilizing the movement and ensuring proper form:

• Shoulder Joint: The shoulder joint (glenohumeral joint) should remain relatively stable throughout the bicep curl. While the biceps brachii does cross the shoulder joint and can contribute to shoulder flexion, in a standard bicep curl, minimizing shoulder movement helps to isolate the work to the elbow flexors. Excessive swinging or "cheating" involves unwanted shoulder flexion and reduces the effectiveness of the exercise for the biceps.
• Wrist Joint: The wrist joint should be held in a neutral or slightly extended position (dorsiflexion) to maintain a strong grip on the weight. It performs an isometric contraction (muscle tension without significant joint movement) to stabilize the hand and transmit force from the weight to the forearm. Unnecessary wrist flexion or extension during the curl can lead to wrist strain or reduce the efficiency of force transfer to the elbow flexors.

Optimizing Your Bicep Curl Technique

To ensure you are effectively targeting the intended muscles through correct joint action:

• Control the Movement: Avoid swinging the weight. Focus on a slow, controlled concentric (lifting) phase, emphasizing elbow flexion, and an equally controlled eccentric (lowering) phase.
• Isolate the Elbow: Keep your elbows tucked close to your sides and minimize movement at the shoulder joint. This ensures the bicep and other elbow flexors are doing the majority of the work.
• Full Range of Motion: Allow for full elbow extension at the bottom of the movement (without hyperextending) and full flexion at the top to maximize muscle recruitment and development.

Conclusion

In summary, the bicep curl is fundamentally an exercise in elbow flexion performed at the elbow joint. This hinge-type joint, powered primarily by the biceps brachii, brachialis, and brachioradialis muscles, allows the forearm to move towards the upper arm. By understanding this specific joint action and ensuring proper stabilization of the shoulder and wrist, you can optimize your bicep curl technique for maximum effectiveness and injury prevention.