Hammer Curls vs Bicep Curls: What Each One Actually Builds
Both exercises bend the elbow, so both train the elbow flexors, but the grip shifts the emphasis. A standard bicep curl, palms facing up, puts the biceps brachii in its strongest position because the biceps also turns the palm upwards. A hammer curl, thumbs up and palms facing each other, takes some of that advantage away and shifts more of the work to the brachialis, which sits under the biceps, and the brachioradialis, the large muscle on the thumb side of the forearm. If you want the peak of the upper arm, prioritise the standard curl. If you want thicker-looking arms and stronger forearms, the hammer curl does more. Most people benefit from doing both.
Most people also use more weight on the hammer curl. That is not a sign it is better, just that the neutral grip is a stronger position for the elbow flexors working together.
The three muscles involved
Biceps brachii
The visible muscle on the front of the upper arm. It bends the elbow and also rotates the forearm so the palm faces up. That second job is why a palms-up grip suits it best: it is fully engaged in both of its roles.
Brachialis
Underneath the biceps, attached lower down on the forearm. It bends the elbow whatever the grip, which makes it a reliable workhorse. A well-developed brachialis can push the biceps outward slightly, which adds to the overall thickness of the arm when viewed from the side.
Brachioradialis
The big muscle running down the top of the forearm from just above the elbow. It works hardest when the forearm is midway between palm up and palm down, which is exactly the hammer grip. This is the muscle that gives the upper forearm its shape.
Side-by-side
| Bicep curl (palms up) | Hammer curl (thumbs up) | |
|---|---|---|
| Main emphasis | Biceps brachii | Brachialis and brachioradialis |
| Typical load | Lighter | Heavier |
| Wrist comfort | Can strain some wrists and elbows | Usually more comfortable |
| Visual effect | Front of the upper arm | Arm thickness and upper forearm |
| Carryover | Chin-ups, underhand pulls | Grip, carries, neutral-grip rows |
How to do each one properly
The bicep curl
- Stand tall, dumbbells by your sides, palms forward.
- Keep your upper arms still, elbows close to the ribs.
- Curl up until the forearm is close to vertical. Squeeze for a moment.
- Lower over two or three seconds until the arm is straight.
Swinging is the usual fault. If your torso rocks or your elbows drift forward, the weight is too heavy. Our article on bicep curl form deals with that in detail.
The hammer curl
- Stand tall, dumbbells by your sides, palms facing your thighs.
- Curl up with the thumbs leading, keeping the wrist straight.
- Stop when the forearm is near vertical. Do not let the elbow swing forward to finish.
- Lower slowly to a straight arm.
The common mistake here is curling across the body towards the opposite shoulder. That variation exists, but it changes the exercise. Keep the dumbbell travelling straight up, in line with the shoulder.
Does it matter which one you choose?
Less than people think. For most adults training two or three times a week, arm size depends far more on the big compound lifts, total weekly volume and consistency than on curl variation. Rows, pulldowns and chin-ups already train the elbow flexors heavily. If the goal is bigger arms overall, see how to build bigger arms without living on curls; triceps make up the larger share of upper arm size.
Where the choice does matter:
- Elbow or wrist discomfort. Many people find the palms-up position aggravates the inside of the elbow or the wrist. A neutral grip is usually kinder.
- Grip and forearm goals. Climbers, rowers, racquet players and anyone who carries heavy shopping up stairs gets more from hammer curls.
- Chin-up strength. The standard curl has more direct carryover to underhand pulling.
Other grip options worth knowing
Between the two extremes sit a few useful variations. The reverse curl, palms facing down, shifts even more work to the brachioradialis and the wrist extensors on the back of the forearm; it is humbling, and you will need a much lighter weight. The incline dumbbell curl, done lying back on an inclined bench, starts the biceps in a stretched position and is hard work at the bottom of the range. A rope hammer curl on a low cable keeps tension where the dumbbell version goes slack. None of these is essential. They are simply options for adding variety, or for working around a sore wrist or elbow, once the basics are in place.
A simple way to use both
An easy approach for a two-session upper-body week:
- Session one: standard dumbbell curl, 2 to 3 sets of 8 to 12.
- Session two: hammer curl, 2 to 3 sets of 8 to 12.
Or alternate them within a single session if time is short. Stop each set one or two reps before form breaks. Add weight when you hit the top of the range on every set. Cable versions with a rope (hammer) or straight bar (standard) also work well and keep tension through the whole movement.
Check with your GP first if you have ongoing elbow or wrist pain, a heart condition, or are coming back to training after a long break. The NHS recommends muscle-strengthening activity on at least two days a week, and arm work can be one small part of that, not the centrepiece.
How we programme arms in the studio
In private sessions at our Archway Road studio, curls are usually a short finisher after the main lifts. If a client has elbow niggles, the hammer grip comes first. If they are working towards their first chin-up, standard curls get more priority. We have a full dumbbell rack and a two-stack cable station, so small weight jumps and grip changes are easy. If you would like a programme built around what you actually want your arms to do, look at our private personal training in Highgate.
Questions we get asked
Are hammer curls better for bigger arms?
They add thickness through the brachialis and forearm. Combined with standard curls and triceps work, they help overall size.
Why can I lift more on hammer curls?
The neutral grip lets the elbow flexors work together in a strong position. That is normal.
Should beginners do curls at all?
A small amount is fine, but compound pulling exercises should come first.
Can I do hammer curls with a cable?
Yes, with a rope attachment on a low pulley. It keeps tension at the bottom of the range. Ask about it in a session; details are on our training page.
Book with The Highgate House
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