Hammer time Hammer curls and the 'secret' for bigger upper arms

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Hammer curls are an exercise for both your lower and upper arms. All in all, it’s not a real biceps exercise, but it does help you make your biceps look bigger.


Hammer curls are very similar to conventional dumbbell curls, in which you rotate your arm out (supinate). Only now you keep your arms in the neutral position (palms facing each other) continuously, as if you were holding a hammer. This shifts the focus from your biceps (upper arm) to your brachioradialis (forearm) muscle , which rises from your humerus. In addition, you train the brachialis muscle (upper arm), so the lower biceps.

The biceps itself also participates, but to a relatively small extent: with a neutral grip you will never get the peak contraction in your biceps that you get with a supinated grip (palms up).

biceps anatomyThe anatomy of the arm (front). Hammer curls primarily train the arm radius (brachioradialis muscle: 2), a muscle in your forearm, and lower biceps (brachialis muscle: 1). (Source: Fotolia)

So are hammer curls not really suitable for larger upper arms? It depends. They may do relatively little for the size of your biceps, but they can develop the top part of your biceps (the “peak”). And that can be important for aesthetic reasons. It is important that you mainly focus on the brachialis during the exercise. We’ll see how you do that in a moment.


You can perform hammer curls standing or sitting. And you can train both arms at the same time or alternately.

With a pair of dumbbells in your hands, keep your arms at your sides, palms facing each other. Now ‘curl’ one or both dumbbells up at the same time by bending your elbow. Stop when your elbow is fully bent. Don’t let your elbow come forward; this takes the tension off your muscles. Now lower the weight in a controlled manner until your elbow is fully extended and repeat for the desired number of reps. Avoid swinging the dumbbell!


Where you hold the dumbbell affects the effect of the exercise. There are two logical options: in the middle or at the top. In the latter case, the top weight of the dumbbell rests on your hand. As a result, you need less grip strength during the performance and you therefore reduce the role of your forearm in favor of your upper arm. If you want to strengthen your grip strength as well as increase your upper arm, you can use both grips, for example two sets with the grip in the middle first and then two sets with the grip at the top.

In addition to dumbbells, you can also perform hammer curls in a cable station, with a rope. Another option is to perform the exercise with kettlebells.


If you hold the dumbbells against the tops of your legs, you skip a little bit of ‘redundant’ ROM that comes at the expense of continuous tension, which is especially important in this exercise (see below).

hammer-curls-romBetter ROM by holding the dumbbells against the top of the legs in the starting position. (Source: YouTube: Paul Carter)


Hammer curls are ideally suited to train the brachialis muscle, which, as we have already seen, is hidden under your biceps. If you develop this muscle well, it pushes your biceps upwards, which ensures a better biceps peak and thus, especially optically, a larger size of your upper arms.

Two adjustments to the exercise shift the emphasis even more to the brachialis, at the expense of the brachioradialis and the biceps themselves:

  • perform the exercise slowly;
  • move to the center of your chest.


Performing the hammer curl relatively slowly increases the activity of the brachialis. The role of the biceps itself then becomes (even) smaller (and thus becomes greater the faster you perform the exercise). This is because the brachial muscle, as research says, only comes into action with sufficient stimulation, namely with slow movements and isometric strength. The brachialis is believed to contain more so  called slow-twitch (type I) muscle fibers, which contract more slowly than type II ( fast-twitch) muscle fibers.

Perform the upward movement relatively slowly, squeezing your muscles well. Hold that muscle tension at the top for two seconds (called a peak contraction), then slowly lower the weight. Do not pause at the bottom, but immediately move on to the next rep.

Below you can see this slow version in the cable version. In the last rep, the brachialis gets an extra boost by applying an even longer peak contraction (namely ten to twenty seconds).


By moving not straight forward, but towards the middle of your chest, you put even more emphasis on the brachialis. From a neutral grip, you move to an almost pronated grip (palm down) that precisely follows the direction of the brachial muscle fibers – more so than reverse curls, where you use a fully pronated grip. Hold the dumbbell as close to your chest as possible. This variant is also called cross-body or cross-over hammer curl.


An effective variation on the standing or seated hammer curl is this reverse incline hammer curl. As the name suggests, you perform it on an incline bench, in a position of 60 to 70 degrees and with your chest on the bench. As a result, you switch off the ‘help’ of your front shoulders and the tension is therefore completely on the muscles in your arms. This performance would additionally increase the involvement of the often neglected long head of the biceps (brachii longus).


Slow hammer curls that move inward instead of forward are the most effective brachial muscle exercise in our opinion. In principle, this exercise should be sufficient for a well-developed brachialis, because the muscle is already trained with ‘normal’ curls.

But if you still want to give it some more targeted training, you can do the aforementioned reverse curls. Also with pull-ups with a very narrow grip (hands together) the brachialis is stimulated. If this exercise is too hard for you, you can also do narrow grip inverted rows.


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