one arm bigger than the other

What To Do If You Have One Arm Bigger Than The Other

If you’ve been working out for a while, you might have noticed a size difference in the muscle mass of your arms. Perhaps you can see that one arm is bigger than the other while looking in the mirror, or that it’s not just a difference in size, but in strength also while you’re lifting weights.

Well, this is perfectly normal. In fact, most people will have some degree of an imbalance when it comes to their arms and this is because one will be more dominant than the other. If you’re right-handed, it’s likely that your right arm will be slightly stronger, and maybe bigger than your left. 

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This can be for a variety of reasons but the main one is simply that you’ll use this hand (and thus arm) more throughout the day to perform regular tasks like carrying things, meaning this arm is being worked more than the other.

It’s also likely that you’re using your dominant side more while performing muscle-building exercises. For example, if you’re performing barbell curls and things get very challenging at the end of a set, your dominant arm might start doing more of the work while your non-dominant one struggles to keep up.

So, even if you feel there is a huge difference between the size of your arms, there are ways you can fix this. Here, we’ll run through the best things to do if one arm is bigger than the other.

What To Do If You Have One Arm Bigger Than The Other

The first thing to do is to not worry. As mentioned above, physical asymmetry is perfectly normal. If the difference in size is an issue for you, then there are several ways you can address it.

The most important change you can make is to switch to unilateral exercises, which means movements that work each arm separately. Barbell exercises and resistance machines will use both arms at the same time, which can lead to muscle imbalances if one arm is doing more work than the other.

By isolating each arm, for example by performing dumbbell curls instead of barbell ones, you’re able to ensure your smaller arm is doing just as much work. There are two main ways to use unilateral exercises to address muscle imbalances.

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The first is to simply perform more sets with your weaker arm than with the other. So, if you’re aiming to perform three sets of bicep curls with both arms, after you’ve completed these then perform one or two more sets with your smaller arm.

Eventually, lifting weights in this way will help even out the size and strength differences in your arms. This is safer than simply lifting a heavier weight with your weaker arm compared to the other, as this could lead to a bicep injury if you were performing curls, for example.

The other method is to perform alternating movements with your arms until your weaker one is exhausted. So, you begin the set with this smaller arm – let’s say you’re doing dumbbell curls. You’d perform one rep with your smaller arm, then one rep with the other arm. You keep going until your weaker arm is exhausted and can no longer keep proper form. 

That is the point you stop the set, even if you feel your other arm could perform several more reps. The logic is that your smaller arm will eventually become just as strong as the other so that they reach the point of exhaustion at the same time.

8 Exercises For One Arm Bigger Than The Other

1. Alternating Dumbbell Curls

How to do it

  1. Hold a dumbbell in each hand with your palms facing each other.
  2. Bend at the elbow on your weaker arm to curl the weight up to your chest, turning your hand so that your palm faces your chest at the top of the movement.
  3. Lower the weight back down and repeat on the other arm.

2. Hammer Curls

How to do it

  1. This is the same movement as traditional curls except that you’re not rotating your hand during the movement; your palms stay facing each other throughout.
  2. Keep your elbows pinned to your body and don’t use anything other than your arms to move the weight.
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3. Dumbbell Shoulder Press

How to do it

  1. Adjust a bench so that it’s at a 90-degree angle like a chair.
  2. Sit with your back against the bench, holding two dumbbells over your shoulders with an overhand grip, elbows bent.
  3. Extend your arms to push the weights above your head, then return them to the starting position.
  4. You could also perform this movement one arm at a time, alternating after each rep.

4. Overhead Tricep Extension

via Gfycat

How to do it

  1. Hold a dumbbell behind your head with one hand so that your elbow is bent and your palm is facing the back of your head.
  2. Straighten your arm to lift the weight up, but don’t lock your elbow out.
  3. Hold, then return the weight back down behind your head and repeat.
  4. Once you’ve completed the desired reps, do the same with the other arm.

5. One Arm Preacher Curls

How to do it

  1. Sit at a preacher bench and hold a dumbbell with one hand, your arm extended out in front and resting on the pad.
  2. Keeping your upper arm against the pad, bent at the elbow to curl the weight up toward you.
  3. Lower back down and repeat for reps, then do the same with the other arm.

6. One Arm Lateral Raise

How to do it

  1. Hold a dumbbell by your side with an overhand grip, palm facing inward.
  2. Keep your other hand on your hip for stability.
  3. Raise the arm holding the weight until it becomes level with your shoulders, keeping the arm extended with a slight bend in the elbow.
  4. Lower back down and repeat for reps, then switch sides.

7. One Arm Bench Press

How to do it

  1. Lie on a flat bench with your feet flat on the ground.
  2. Hold a dumbbell in one hand just above your chest with your elbow bent.
  3. Push the weight up and extend your arm, then lower back down and repeat.
  4. Once all reps are completed, switch to the other arm.
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8. One Arm Dumbbell Row

via Gfycat

How to do it

  1. Stand next to a flat bench, facing parallel, and place your right knee and right hand on it so that you’re bent over, with your left leg straight and left foot flat on the ground.
  2. Hold a dumbbell in your left hand, palm facing inward and arm extended so the weight hands below your chest.
  3. Squeeze your shoulder blades together and pull the weight up into your midsection, then lower it back down. Repeat and then switch sides.


Having one arm bigger than the other is nothing to worry about as it’s a perfectly normal occurrence and happens to many people, particularly those new to regular training and exercise. If you do notice you have a slight muscle imbalance in your arms, focus on performing unilateral exercises, ensuring your smaller arm is properly exhausted. If you do this consistently, the asymmetry should eventually even out.

Frequently Asked Questions

Is it bad if one arm is bigger than the other?

If it is only slightly bigger and only you can notice, then it’s no bad thing. There will almost always be imbalances in your body – for example, a lot of people have one arm longer than the other – and they’re not inherently bad for you. However, you don’t want there to be too much of a difference in arm size, as this can affect things like your posture and other muscle groups.

Do muscle imbalances fix themselves?

Unfortunately not. Muscle imbalances usually occur through our everyday movements and posture and so if left unattended they’re more likely to get worse rather than fix themselves. So, if you notice imbalances, try to address them.

How do you fix uneven deltoids?

Your deltoids are your shoulder muscles, and if there’s an imbalance between them then you can fix this in the same way as explained above; using unilateral exercises. Exercises like the overhead press, lateral raise, front raise, and push press all recruit the deltoid muscles and will help fix any differences in size.

George Gigney

George is a Level 3 Personal Trainer and qualified Behavior Change Specialist. He has been training clients for several years and writing for over a decade, focusing on sport, wellbeing, and fitness.

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