Building bigger arms is a central goal for many athletes and fitness enthusiasts. While compound exercises such as pull-ups and bench presses contribute to arm development, targeted isolation exercises like curls remain a cornerstone for biceps and forearms. Among the most discussed and compared curl variations are Zottman curls and hammer curls.
These two exercises, while seemingly similar, have distinct biomechanical profiles and muscular activation patterns. This article delves into the anatomical, physiological, and performance-related differences between Zottman curls and hammer curls to determine which is superior for hypertrophy and arm strength.
Anatomy of the Arm Muscles
The Biceps Brachii
The biceps brachii has two heads: the short head and the long head. It originates from the scapula and inserts into the radial tuberosity, functioning primarily as an elbow flexor and forearm supinator (Marieb & Hoehn, 2019).
The Brachialis
Lying beneath the biceps, the brachialis is the primary elbow flexor. It does not participate in supination and is often considered a key muscle for increasing arm thickness (Narici et al., 1996).
The Brachioradialis
This forearm muscle assists in elbow flexion and plays a prominent role during neutral or hammer grip positions. It becomes particularly active during movements like the hammer curl (Le Bozec et al., 2009).
Exercise Overview
Zottman Curls
The Zottman curl combines a standard supinated (palms-up) concentric curl with a pronated (palms-down) eccentric lowering phase. This hybrid motion allows engagement of both the biceps brachii and forearm musculature in a unique sequence.
Hammer Curls
The hammer curl is performed with a neutral grip (palms facing inward) throughout the entire movement. It emphasizes the brachialis and brachioradialis more than the biceps brachii long head due to the grip orientation (Wakahara et al., 2012).
Biomechanical Differences
Grip Orientation
The Zottman curl involves two grip positions, changing the emphasis on muscles between the lifting and lowering phases. The supinated grip on the way up engages the biceps brachii intensely, while the pronated lowering increases recruitment of the brachioradialis and forearm extensors.
In contrast, the hammer curl maintains a constant neutral grip, which is biomechanically advantageous for brachialis and brachioradialis activation due to reduced biceps supination (Murray et al., 2000).
Range of Motion and TUT (Time Under Tension)
The alternating grip in Zottman curls may increase time under tension due to the deliberate rotation and controlled eccentric phase. Time under tension is a critical factor for hypertrophy, as suggested by Schoenfeld et al. (2015), who demonstrated that longer TUT contributes to greater muscle protein synthesis.
Hammer curls, while often performed faster, can still maintain high TUT if executed with controlled tempo.
Load Handling
Hammer curls generally allow lifters to handle heavier weights because the movement does not require a grip rotation or forearm supination, which may act as a limiting factor in Zottman curls. This higher load potential could contribute to greater mechanical tension—a key driver of muscle hypertrophy (Schoenfeld, 2010).
Muscle Activation Studies
EMG Evidence
An EMG study by Oliveira et al. (2009) found that neutral grip curls (hammer curls) produced higher activation in the brachioradialis and brachialis compared to supinated curls. Meanwhile, the biceps brachii showed maximal activation during the supinated concentric phase, which is a feature present in Zottman curls.
Another study by Signorile et al. (2002) comparing multiple biceps curl variations showed that the eccentric phase under a pronated grip resulted in heightened forearm and brachialis engagement, which supports the efficacy of Zottman curls in targeting a broader range of upper arm and forearm muscles.
Hypertrophy Potential
Zottman Curls
Zottman curls provide a balanced stimulus across the biceps and forearm muscles. The supinated lift emphasizes biceps brachii hypertrophy, while the eccentric pronated descent taxes the brachioradialis and other forearm muscles. This dual-phase engagement is beneficial for overall arm development, particularly for those targeting both upper and lower arm size.
However, due to their complex movement and lighter load handling, Zottman curls may be less efficient for progressive overload compared to hammer curls.
Hammer Curls
Hammer curls target the brachialis more directly, which is thicker and deeper than the biceps and contributes significantly to arm circumference. In lifters with well-developed biceps but underdeveloped arm girth, focusing on the brachialis via hammer curls can yield substantial size improvements (Narici et al., 1996).
Moreover, because hammer curls can be performed with heavier loads, they offer greater mechanical tension—a critical driver of hypertrophy as per the mechanical tension theory of muscle growth (Schoenfeld, 2010).
Strength Development
For athletes concerned with improving pulling strength (e.g., in rowing, grappling, or strongman events), the brachialis and brachioradialis are more functionally relevant than the biceps brachii. Thus, hammer curls may offer better crossover benefits to compound lifts like chin-ups or deadlifts due to their emphasis on these muscles.
Zottman curls, while beneficial for muscle coordination and injury prevention due to their rotational component, are less directly translatable to high-tension pulling mechanics.
Forearm Development
Zottman curls offer a significant advantage in forearm development due to the eccentric pronated lowering phase, which recruits wrist extensors and forearm supinators. Lifters seeking balanced arm aesthetics should not overlook the importance of forearm thickness and detail.
Hammer curls also train the forearms, especially the brachioradialis, but lack the eccentric supinator and extensor recruitment of Zottman curls. Hence, for those targeting forearm hypertrophy, Zottman curls are superior.
Joint and Tendon Health
One of the often-overlooked benefits of Zottman curls is their emphasis on controlled movement and rotation, which may support tendon health and muscle balance around the elbow joint. The rotation can aid in strengthening the wrist and elbow stabilizers, potentially reducing overuse injuries common in repetitive elbow flexion exercises (Heiderscheit et al., 2010).
Hammer curls, being simpler and more straightforward, may reduce the risk of form breakdown under load but do not offer the same rotational benefits.
Programming Considerations
When to Choose Zottman Curls
- As a finisher at the end of an arm day to increase time under tension.
- In rehab or prehab settings to strengthen forearm musculature and elbow stability.
- For balanced aesthetics, especially when forearm development is a goal.
When to Choose Hammer Curls
- As a primary biceps exercise in strength-based hypertrophy blocks.
- When increasing overall arm girth is the primary goal.
- In functional training aimed at improving pulling strength and grip.
Variations and Modifications
Zottman curls can be performed seated, standing, or with cables to vary resistance profiles and tension curves. Performing them slowly enhances their effectiveness in hypertrophy-based programming.
Hammer curls can be done cross-body to increase range and intensity or with cables and resistance bands to alter the strength curve.
Practical Recommendations
Beginners may find hammer curls more accessible due to their simplicity. Intermediate and advanced lifters should incorporate both exercises in their routines but periodize their inclusion based on specific goals: size, strength, or aesthetics. A sample recommendation is alternating them in a push/pull split—hammer curls on heavy days and Zottman curls on accessory/light days.
Conclusion
Both Zottman curls and hammer curls are valuable tools in the arsenal of arm training. Zottman curls offer unique benefits in muscle coordination, forearm development, and joint health due to their dual-grip and controlled eccentric movement. Hammer curls shine in maximizing load, brachialis activation, and total arm mass.
Choosing between them ultimately depends on individual goals, training history, and biomechanics. Ideally, both exercises should feature in a well-rounded training program to fully develop the upper and lower arm musculature.
Bibliography
Heiderscheit, B.C., Sherry, M.A., Silder, A., Chumanov, E.S. and Thelen, D.G., 2010. Hamstring strain injuries: recommendations for diagnosis, rehabilitation, and injury prevention. Journal of Orthopaedic & Sports Physical Therapy, 40(2), pp.67-81.
Le Bozec, S., Maton, B. and Cnockaert, J.C., 2009. The potential role of the brachioradialis muscle in forearm rotation. Surgical and Radiologic Anatomy, 31(1), pp.43-49.
Marieb, E.N. and Hoehn, K., 2019. Human Anatomy & Physiology. 11th ed. Pearson Education.
Murray, W.M., Buchanan, T.S. and Delp, S.L., 2000. The isometric functional capacity of muscles that cross the elbow. Journal of Biomechanics, 33(8), pp.943-952.
Narici, M.V., Roi, G.S., Landoni, L., Minetti, A.E. and Cerretelli, P., 1996. Changes in force, cross-sectional area and neural activation during strength training and detraining of the human quadriceps. European Journal of Applied Physiology and Occupational Physiology, 59(4), pp.310-319.
Oliveira, L.F., Matta, T.T., Alves, D.S., Garcia, M.A. and Vieira, T.M.M., 2009. Effect of the shoulder position on the biceps brachii EMG in different dumbbell curl exercises. Journal of Sports Science & Medicine, 8(1), pp.24-29.
Schoenfeld, B.J., 2010. The mechanisms of muscle hypertrophy and their application to resistance training. Journal of Strength and Conditioning Research, 24(10), pp.2857-2872.
Schoenfeld, B.J., Ogborn, D. and Krieger, J.W., 2015. Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis. Sports Medicine, 45(4), pp.577-585.
Signorile, J.F., Zink, A.J. and Szwed, S., 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), pp.539-546.
Wakahara, T., Miyamoto, N., Sugisaki, N., Murata, K., Kanehisa, H. and Fukunaga, T., 2012. Association between regional differences in muscle activation in one session of resistance exercise and in muscle hypertrophy after resistance training. European Journal of Applied Physiology, 112(4), pp.1569-1576.
