Hammer Curls vs. Regular Curls: Which is Better for Mass?

When it comes to building bigger arms, biceps curls are the go-to movement for most lifters. But within the realm of curls, there is significant variation, and two of the most commonly compared are hammer curls and regular curls.

Both exercises aim to target the biceps and other muscles of the upper arm, but they differ in technique, muscle recruitment, and ultimately, their hypertrophic outcomes. This article breaks down the anatomy, mechanics, and scientific evidence behind both movements to determine which is better for building muscle mass.

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Understanding the Anatomy of the Arm

Biceps Brachii

The biceps brachii is a two-headed muscle consisting of a long head and a short head. Both heads originate at different parts of the scapula and insert on the radial tuberosity of the forearm. The primary functions of the biceps brachii include elbow flexion and forearm supination.

Brachialis

Sitting underneath the biceps brachii, the brachialis is a powerful elbow flexor and often overlooked in training discussions. It attaches to the humerus and inserts onto the ulna, giving it a biomechanical advantage during elbow flexion, particularly when the forearm is in a neutral or pronated position.

Brachioradialis

This muscle of the forearm plays a role in elbow flexion, especially when the wrist is in a neutral position. It also assists in stabilizing the elbow during lifting movements.

Hammer Curls: Mechanics and Muscle Recruitment

Execution

Hammer curls are performed with the palms facing each other throughout the movement, typically using dumbbells. The neutral grip reduces supination of the forearm and alters the recruitment pattern compared to regular curls.

Target Muscles

Due to the grip and wrist positioning, hammer curls engage the brachialis and brachioradialis more heavily than standard biceps curls. The biceps brachii are still involved but take a slightly secondary role compared to the other two muscles.

Biomechanical Considerations

The neutral grip shortens the biceps’ range of motion slightly, especially in terms of supination, but enhances the mechanical load on the brachialis. Since the brachialis has a greater cross-sectional area potential than the biceps brachii, this muscle is critical for overall arm mass.

Regular Curls: Mechanics and Muscle Recruitment

Execution

Regular curls, often called supinated curls, involve turning the palms up (supinated grip) throughout the movement. This is the classic curl motion seen in gyms and often performed with dumbbells, barbells, or cables.

Target Muscles

The supinated grip heavily recruits both heads of the biceps brachii. Forearm supination, combined with elbow flexion, places maximum stress on the biceps. The brachialis and brachioradialis are still involved but less so compared to hammer curls.

Biomechanical Considerations

The supinated position maximizes biceps activation, particularly the long head, which is more involved when the shoulder is also slightly flexed. This results in greater muscle tension and metabolic stress, both important for hypertrophy.

Hypertrophy Potential: Hammer Curls vs. Regular Curls

Muscle Fiber Recruitment

Research indicates that the brachialis may have a higher proportion of Type II (fast-twitch) fibers than the biceps brachii, making it more responsive to hypertrophic stimuli from heavy or moderate-load training. Hammer curls, by emphasizing this muscle, can therefore be highly effective for mass gain (Narici et al., 1989).

In contrast, regular curls provide greater activation of the biceps brachii due to their inclusion of forearm supination and elbow flexion. According to a study by Oliveira et al. (2009), exercises that combine these movements maximize electromyographic (EMG) activity in the biceps.

Time Under Tension

Hammer curls allow for heavier loading and greater control due to the neutral grip, which can translate to increased time under tension (TUT). TUT is a recognized hypertrophy mechanism, especially when performed with controlled eccentric phases (Schoenfeld, 2010).

Regular curls, on the other hand, provide a longer range of motion and greater peak contraction in the biceps. This may enhance the stretch-mediated hypertrophy component, another important factor in muscle growth (Wackerhage et al., 2019).

Progressive Overload and Strength Transfer

Because hammer curls typically allow for greater loads, they may be more beneficial for progressive overload, especially for the brachialis and brachioradialis. Stronger brachialis development indirectly supports heavier lifting in compound movements such as rows and pull-ups.

Regular curls may not permit the same loading, but they offer a direct and isolated biceps stimulus, ideal for muscle-specific hypertrophy and aesthetic development. The peak contraction achieved in the supinated curl is difficult to replicate with hammer curls, making regular curls potentially better for peak biceps shaping.

Comparative Studies and EMG Research

A study by Signorile et al. (2002) compared EMG activity of the biceps brachii, brachialis, and brachioradialis across different curl variations. The results showed that regular curls produced the highest biceps brachii activation, while hammer curls elicited greater brachialis and brachioradialis involvement.

Another investigation by Mausehund et al. (2020) confirmed that hand position significantly alters muscle activation patterns. The neutral grip (used in hammer curls) increased brachialis and brachioradialis activity without significantly reducing biceps activation, making it a valuable complement to regular curls.

Practical Application: Programming for Mass

Exercise Selection

To maximize overall arm hypertrophy, both hammer curls and regular curls should be included in a comprehensive training program. While regular curls are ideal for targeting the biceps directly, hammer curls build thickness and support around the arm by developing the brachialis and forearms.

Volume and Frequency

For hypertrophy, a weekly volume of 10-20 sets for biceps and associated muscles is generally effective (Schoenfeld et al., 2016). Splitting this volume between hammer and regular curls ensures balanced development. For example:

• 3 sets of hammer curls twice per week
• 3 sets of regular curls twice per week

Load and Rep Range

Both exercises respond well to moderate (8-12 reps) and higher (12-15 reps) repetition ranges. However, hammer curls may also benefit from slightly heavier loads due to the stronger grip and reduced wrist torque. Regular curls, with their emphasis on control and peak contraction, should prioritize form and full range of motion.

Injury Prevention and Joint Health

Wrist and Elbow Considerations

Hammer curls are generally easier on the wrists due to the neutral grip, making them a good option for individuals with wrist discomfort. They also reduce supination stress, which can exacerbate issues in the distal biceps tendon.

Regular curls, while more demanding on wrist positioning, are safe and effective when performed with proper form. Rotating implements, like dumbbells or cables, may reduce strain and accommodate natural wrist movement.

Tendon Health

Balanced training of the biceps brachii and brachialis reduces the risk of muscular imbalances that can lead to overuse injuries. A study by Seitz et al. (2014) noted that tendon loading varies between grips and positions, suggesting that alternating exercises like hammer and regular curls may benefit long-term joint integrity.

Conclusion: Which is Better for Mass?

The answer depends on your specific goals. For pure biceps size and peak development, regular curls are slightly superior due to their higher biceps activation and peak contraction. However, for total arm mass, hammer curls offer a more comprehensive stimulus by engaging the brachialis and brachioradialis more significantly. Ultimately, the best approach is to incorporate both exercises into a hypertrophy-focused program to ensure balanced development and maximize muscle-building potential.

Bibliography

Mausehund, L., Christiansen, D., & Seynnes, O. (2020). The Influence of Handgrip Position on Muscle Activation During the Dumbbell Curl. European Journal of Sport Science, 20(3), 312-318.

Narici, M. V., Roi, G. S., & Landoni, L. (1989). Force and Power Characteristics of Quadriceps in Children and Adults. European Journal of Applied Physiology and Occupational Physiology, 59(3), 195-200.

Oliveira, L. F., et al. (2009). EMG Analysis of Biceps Brachii Muscle During Different Curl Exercises. Journal of Sports Science & Medicine, 8(4), 529-534.

Schoenfeld, B. J. (2010). The Mechanisms of Muscle Hypertrophy and Their Application to Resistance Training. Journal of Strength and Conditioning Research, 24(10), 2857-2872.

Schoenfeld, B. J., Ogborn, D., & Krieger, J. W. (2016). Dose-Response Relationship Between Weekly Resistance Training Volume and Increases in Muscle Mass: A Systematic Review and Meta-Analysis. Journal of Sports Sciences, 35(11), 1073-1082.

Seitz, L. B., et al. (2014). Effects of Supination and Grip Width on Muscle Activation During Elbow Flexion Exercises. Journal of Strength and Conditioning Research, 28(5), 1229-1236.

Signorile, J. F., Zink, A. J., & Szwed, S. P. (2002). A Comparative Electromyographical Investigation of Muscle Utilization Patterns Using Various Hand Positions During the Lat Pull-Down. Journal of Strength and Conditioning Research, 16(4), 539-546.

Wackerhage, H., Schoenfeld, B. J., Hamilton, D. L., et al. (2019). Stimuli and Sensors That Initiate Skeletal Muscle Hypertrophy Following Resistance Exercise. Journal of Applied Physiology, 126(1), 30-43.

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