What part of biceps do hammer curls work?

Hammer curls are an excellent exercise to build big biceps and forearms. They also add to arm size by working the brachialis — a small but crucial muscle engulfed between the biceps and triceps.

The biceps are anatomically referred to as the 'biceps brachii', a Latin term that translates to 'two headed muscle of the arm". The biceps has two distinct heads — the long and short head — which originate from the supraglenoid tubercle of the scapula and the coracoid process of the scapula, respectively.

Both heads have a common insertion point at the radial tuberosity and forearm fascia, via bicipital aponeurosis aka lacertus fibrosis. This unique anatomical structure allows the biceps to perform the following functions:

• Elbow flexion - Helps in bending the arm at the elbow joint. A classic example is when you perform a bicep flex to show off your guns.
• Forearm supination - Aids in rotation of the forearm and hand. For eg, when you open a door by turning a key.
• Shoulder flexion - enhances the dynamic stability of the shoulder joint in the initial 30 degress of elevation. That helps you carry heavy weights when the arm is extended downward.

The biceps are actively involved in curling and pulling movements, such as rows or chin-ups. Interestingly, the smaller brachialis muscle is the most powerful flexor of the forearm, while the biceps largely play a stablizing role.

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Which biceps part do hammer curls work?

Now that we've covered the basic anatomy of the biceps, let's move to the question at hand.

Hammer curls target both heads of the biceps, as well as the brachialis, and brachioradialis (located in the forearm). However, the long head is worked to a much greater extent, which is why hammer curls are ideal for building the bicep 'peak'.

They also target the brachialis muscle effectively, giving the arms a more defined, thicker appearance. At lower body fat level, a well-developed brachialis can significantly improve arm aesthetics, and is, therefore, a priority for bodybuilders.

In comparison, regular curls work the shorter head of the biceps more, which contributes to arm width when viewed from the front.

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How to perform hammer curls?

Here's how to do a hammer curl:

• Stand upright with a dumbbell in each hand.
• Hold the dumbbells by your side with stretched arms. Adopt a neutral grip, with your palms pointing towards you.
• As you begin the movement, bend your arms at the elbow joint, and curl the dumbbells upwards as far as possible.
• Hold the contraction at the top of the movement for a second. You will be able to feel your upper arm and forearm muscles tightening, if done properly.
• Lower the dumbbell while controlling the eccentric part of the movement.

Tips:

• Keep you elbows fixed on your sides.
• Brace your core. Avoid leaning back.
• A little bit of momentum is fine as you reach the final 2-3 reps. If you're using body momentum to push the weight up from the starting reps, you are using other muscles and losing bicep muscle activation.
• Drop the weights, and start with something lighter. The joints and tendons will thank you in the future.
• Perform hammer curls in a higher rep range, ideally in the 8-15 range.
• Add them to supersets with tricep exercises like extensions or pushdowns.

When done with correct form, hammer curls help:

• Increase bicep size and strength
• Thicken and strengthen the brachialis and forearm muscles
• Improve wrist mobility and stability
• Increase grip strength

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Takeaway

Hammer curls are an effective movement to build big arms. They help grow the longer head of the biceps and brachialis muscle to a greater degree, while engaging the forearm and short head of the bicep.