Why the grip changes which muscle works hardest
Three muscles bend the elbow. The biceps is strongest when the palm is turned up, because one of its jobs is rotating the forearm into that position. The brachialis, a flat muscle underneath the biceps, does nothing but bend the elbow, so it works in every grip. The brachioradialis runs from just above the elbow down the thumb side of the forearm and has the most leverage when the thumb points up. Turn the palms in and the biceps loses its advantage, so the other two take a larger share.
That is a shift of emphasis, not a different exercise: the biceps still works hard in a hammer curl. The practical case for it has three parts. Most people can handle a little more weight; it trains the forearm and grip along the way; and lifters whose wrists dislike the palms-up position often find the neutral grip easier to live with. It usually comes after a bicep curl, or replaces one on a second arm day. The biceps guide shows how both fit into a week.
Getting set
- Take a pair of dumbbells you can curl for about ten reps. Try your bicep curl weight first; many people find they can go one pair heavier.
- Let them hang at your sides with the palms facing your thighs and the thumbs pointing forward. Hold each handle in the middle, firmly.
- Stand tall with your feet hip width and knees soft. For the strictest version, sit upright on a flat bench, which takes the hips out of it.
- Draw your shoulders back and down and set your elbows against your sides. Wrists are straight, with each dumbbell hanging in line with the forearm.
- Choose both arms together, which is quicker, or alternating, which lets you focus on one arm while the other rests for a moment.
Doing the rep
- Curl the dumbbell up with the thumb leading and the palm still facing inward. Nothing rotates; that is what makes it a hammer curl.
- Move only at the elbow, like a door swinging on its hinge, with the upper arm resting against your side.
- Bring the top end of the dumbbell to roughly the front of your shoulder, then squeeze the handle hard for a moment.
- Lower over about three seconds until the elbow is straight but not snapped into lock.
- If you are alternating, finish the whole rep with one arm before the other starts, so neither swings to help.
Grip the handle as if you were trying to crush it. A hard squeeze recruits more of the forearm, stops the wrist wobbling and tells you clearly when it is the forearm, not the biceps, that is giving out. Breathe out as you lift.
Common hammer curl mistakes
| Mistake | What it looks like | The fix |
|---|---|---|
| Turning the palms up | The thumbs rotate outward as the dumbbell rises and it becomes an ordinary curl | Keep the thumbs pointing at the ceiling at the top of every rep |
| Going too heavy | Because the hammer feels stronger, the load creeps up and the hips start driving it | Stay one pair lighter until every rep is strict |
| Elbows swinging forward | The upper arm lifts and the front of the shoulder finishes the rep | Stop at shoulder height with the elbows still against your sides |
| Loose wrists | The dumbbell tips forward or back and the wrist bends with it | Squeeze hard and keep the dumbbell upright in line with the forearm |
| Rushing the way down | The dumbbells fall back to the thighs between reps | Take about three seconds to lower each one |
Cross-body and rope hammer curls
Both versions keep the neutral grip. One changes the path of the dumbbell; the other moves the exercise to the cable station.
Cross-body hammer curl
Curl one dumbbell up and across your body towards the opposite side of your chest, thumb up, then lower it back to your side. The elbow travels slightly inward while the shoulder stays still. Many lifters feel it more along the outside of the arm, and the dumbbell clears the thigh easily. Work one arm at a time and keep the torso from twisting.
Rope hammer curl on the cable
Clip a rope to the low pulley, hold one end in each hand with palms facing each other, and curl towards your shoulders, letting the ends spread slightly at the top. The cable keeps tension at the bottom, where dumbbells go light, and the stack allows small weight jumps. If you have searched for a hammer curl machine, this is the version most gyms use.
If the dumbbell rack is crowded, the rope version does the same job on the cable station, and the bicep curl page covers the palms-up curls you can do with an EZ bar instead.
Sets, reps and where to put it
| Goal | Sets × reps | How hard |
|---|---|---|
| Learning the movement | 2 × 12 | Stop with three reps left |
| Arm and forearm size | 3 × 8–12 | One or two reps short of failure |
| Grip endurance | 2–3 × 15–20 | A one-second squeeze at the top; last set close to failure |
Rest about a minute between sets, or longer if your grip has not recovered.
Once or twice a week is plenty. If time is short, alternate it with the bicep curl from one week to the next rather than stacking three curl variations into one session. Add reps until every set reaches the top of the range, then move up one pair. Rows, pulldowns and deadlifts tax the grip too, so hammer curls belong after those, never before.
Hammer curls at RPM
RPM's floor photos show a dumbbell rack in the functional zone and multi-station cable towers, so both the dumbbell and the cable versions can be done on the training floor in Al Manhal. Which attachments are on the station, a rope included, is worth asking about on your free tour. If you would like someone to watch your first sets, a personal training session will sort out the grip and elbow position quickly.
Questions, answered.
Hammer curls vs bicep curls: which should I do?
Both, if you can. The bicep curl trains the biceps in its strongest position; the hammer curl shifts more work to the brachialis and forearm. If you only have time for one, alternate them week to week. The bicep curl page covers the palms-up versions.
What muscles do hammer curls work?
The biceps, the brachialis underneath it and the brachioradialis on the thumb side of the forearm, plus the forearm muscles that hold your grip.
Is a hammer curl the same as a reverse curl?
No. A reverse curl uses an overhand grip, palms facing down. It is harder, so you will use noticeably less weight, and the muscles on top of the forearm work more to keep the wrist straight. The hammer sits between the reverse curl and the palms-up bicep curl.
Do hammer curls make your forearms bigger?
They train the brachioradialis, the prominent muscle on the thumb side of the forearm, so they are one of the more direct ways to add forearm work. How much your forearms change depends on your training as a whole, what you eat and how consistent you are.
Can I do hammer curls with a barbell?
Not with a straight bar, which fixes your palms facing forward or down. Some gyms have a multi-grip bar with parallel handles; otherwise the rope on the cable is the closest two-handed version.
Should I do hammer curls if my elbow hurts?
Not until it has been checked. Elbow pain during curls is a reason to stop and see a doctor or physiotherapist, whatever the grip. Some people find the neutral grip more comfortable once they are cleared to train, but that decision comes after the check, not instead of it.