July 19, 2025, 5:02 pm | Read time: 7 minutes
Defined upper arms are a popular training goal. But achieving this requires more than just a strong and visible biceps. The forearms should not be neglected either, to avoid working too one-sidedly and to create a uniform overall appearance. This is where hammer curls come into play, providing a perfect complement to biceps curls. They can lead to even stronger and more muscular arms. Which muscle groups are specifically trained with this exercise, how it works exactly, and how the two curl variants differ from each other is explained by FITBOOK author Tony Poland along with an expert.
Overview
Muscles Trained by Hammer Curls
Hammer curls primarily target three muscle groups. The main target muscle is the brachialis, the so-called Musculus brachialis. This muscle plays a crucial role in elbow flexion and is the strongest flexor in the elbow joint. Anatomically, the brachialis lies beneath the biceps brachii, the classic biceps muscle. This muscle is also engaged during hammer curls, though less isolated than in biceps curls.
Additionally, the focus is on the brachioradialis, the forearm muscle. It is located on the outer forearm and helps define it. “It simply provides a bit of a pump, making the arm look good,” says personal trainer Markus Bremen. The reason is the neutral grip in hammer curls, where the palms face each other.
Even just holding the dumbbells involves the hand and finger muscles, and the shoulder is needed for stabilization.
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Benefits of Hammer Curls
The advantages of this exercise are both functional and aesthetic. Since the main focus is on the brachialis, it naturally becomes stronger. When this happens, it visually pushes the biceps upward, making the arm appear larger or thicker.
Moreover, the neutral grip places significant demand on the forearm muscles, especially the brachioradialis. The result is improved grip strength and stronger forearms, which is very helpful in exercises like deadlifts or pull-ups.
The neutral grip in these curls also makes the exercise more natural for the wrist, thus being joint-friendly. Biceps curls, for example, are performed with a supinated grip (palms facing up), which is much less natural.
Another advantage is that hammer curls can be performed in a variety of ways. Options range from standing or sitting to repetitions on a cable machine or with resistance bands. Hammer curls with both arms simultaneously can also be easily integrated. Ultimately, all variations promote powerful flexion movements, which can have positive effects in everyday life, such as carrying heavy bags.
“It’s a very nice exercise for strengthening the forearms and is therefore advantageous in many sports that rely heavily on grip strength, such as climbing, martial arts, or boxing,” says Markus Bremen.
Hammer curls improve overall arm strength, especially when combined with biceps curls, enhance appearance, and also protect the joints! This results in functionally strong and balanced arms.
How to Perform Hammer Curls Correctly
Hammer curls are usually performed standing, alternating left and right. It is essential to keep the upper body straight and not move it during the exercise. Then, slightly bend the knees, tighten the gluteal muscles, and straighten the back. Hold a dumbbell in each hand with the previously mentioned neutral grip, keeping the elbows close to the body. Now, lift one hand with the palm facing outward, keeping the elbows firmly against the body and the body stable. Just before the dumbbell reaches the upper body, pause briefly at the moment of maximum muscle tension, then lower the weight slowly and controlled back toward the floor. Then smoothly continue with the other side. Important: The entire movement should come solely from the forearms.
In terms of repetitions, three sets of eight to twelve repetitions are a good start. The chosen weight should be manageable. If you only do hammer curls and skip biceps curls, five sets of six to ten repetitions with a slightly higher weight are advisable.
Also Suitable for Beginners
“The exercise is relatively simple to perform and therefore also suitable for beginners. You remain in the neutral position, so the hands are not rotated during the upward movement,” emphasizes the expert. It is important, as already described, not to use momentum, “but to work very dryly and without movement momentum, so that the strength comes optimally from the target muscles and the effect is simply better.”
Hammer curls can also be performed sitting. In this case, make sure to have a straight backrest. This prevents the upper body from rocking. “Sitting, you take significantly more core muscles out of the equation because you don’t have to stabilize yourself and keep your pelvis upright,” says Markus Bremen. Therefore, the exercise is ideal for older clients or for rehab training with seniors.
Hammer Curls: One-Sided or Both Sides?
In the gym, you can observe different variations of hammer curls. They are usually performed either with both arms simultaneously or alternately right and left. There is no right or wrong. “It depends on what you intend to do,” reveals the expert. “When working alternately, you have more core training and a higher focus on the core muscles. The opposite side has to stabilize, especially when the weight increases,” describes Markus Bremen. Additionally, this variant can be used specifically if you want to train one side deliberately.
Performing the exercise with both arms parallel or simultaneously, on the other hand, achieves something different. “In the bilateral execution, you can handle more weight and thus have a higher strength stimulus,” notes Markus Bremen.
Common Mistakes
Improper hammer curls, as is often the case with fitness exercises, reduce the training effect or can lead to injuries. A common problem is using momentum with the upper body. This shifts the focus to other muscles, such as the back, rather than the intended target muscles. So: maintain body tension, focus on a slow and controlled movement, and reduce the weight if necessary.
If the movement comes from the shoulder instead of the forearms, the load also shifts away from the biceps and brachialis. The focus must be on keeping the elbows close to the body.
Additionally, the lowering of the dumbbell should not be too fast, as this sacrifices effectiveness. The muscles work particularly in this eccentric phase. A duration of two to three seconds is a good guideline. A weight that is too heavy is also unfavorable, as the technique usually suffers significantly. You lose control and become imprecise. Finally, avoid a hollow back or a hunched back. Otherwise, the lower back is overly stressed.
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Hammer Curls vs. Biceps Curls: Which Is More Effective for the Upper Arms?
It should be noted that you can train your arms with both curl variants. However, the key question is what you want to focus on. Hammer curls and biceps curls create different training stimuli.
Why Biceps Curls Have the Edge
Basically, one could say that biceps curls are more effective for pushing your biceps to the maximum because they offer more isolation. In contrast, hammer curls, with their increased focus on the brachialis and forearms, promote arm volume. They also enhance grip strength.
Advantages of Hammer Curls
“The biceps curl has a bit more range of motion, so the muscle is trained more in its length. It is also a bit more demanding due to the rotational movement. The hammer curl trains grip strength and is somewhat simpler. And to let the arm grow in its entirety, it is somewhat more effective,” concludes Markus Bremen. By the way: “It is also well-suited as a finisher exercise (an exercise that specifically boosts metabolism after the main workout, providing a longer afterburn effect; editor’s note). If you have a full-body workout, you can finish off the arms with it. Or as a final exercise on arm day, when you specifically train the arms to get a real pump.”
Ideally, you combine biceps curls with hammer curls within a workout: for targeted upper arm muscle development, arm strength, thickness, and functional power.1