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What Should I Do If One Arm Is Bigger Than The Other?

Michael Garrico
Published by Michael Garrico
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: February 26, 2022

As a personal trainer, I have spent a lot of my time making sure that all my clients make steady improvements to their overall physique. And from the earliest stages of a body sculpting effort, I get my clients to pay close attention to their weak side.

My research and experience have shown that there are a few ways to deal with a smaller arm, but it takes careful planning of reps and sets.

There are also a few common mistakes people make, and I'll show you exactly how to avoid those in your biceps exercises.

Quick Summary

  • Most athletes have a slight bias to a stronger arm that might become slightly bigger, but you should avoid a big difference in your upper arms. 
  • There are a few isolation workouts that will help you make the weaker arm bigger. 
  • Avoiding a few simple mistakes should help you disrupt uneven muscle growth.

How Do You Even Out Your Arm Sizes?

man using a tape measure on his biceps

You can even out your arm sizes by focusing more attention on unilateral movements where the non-dominant arm lifts a larger weight load or does an extra set.

That means that you train each arm separately with isolation bicep exercises.

Only one arm is under strain at a time, which allows you to push the weak arm harder than the dominant side.

I'll get to some sample exercises shortly, but the main way to approach this problem is to lift heavier on the weaker arm.

For example, if your left arm is smaller than the right, and you typically curl a 15 lbs dumbbell, then drop the weight on the right arm to 12 lbs.

Or, if you prefer maintaining the same weight, then do one extra set on the weaker side.

That should help your left side catch up.

The other thing I'd say here is that you don't want to think that a few extra reps on your weaker arm will solve the muscle size issue.

It's just not that simple.

Why Do People End Up With One Arm Bigger Than The Other?

stack of dumbbells in the gym and a man with painful elbows

Here are four reasons why you can end up with one arm that's bigger than the other.

Hand Dominance

Everybody has a dominant hand for physical work. It's the hand you naturally use to pick up stuff and use for handwriting [1]. That natural dominance comes from your brain, leading to a dominant arm naturally.

Different Weight Loads

Because of the dominant hand effect above, you can end up loading up a larger weight for one arm over the other when you do isolation exercises.

Gripping a lower weight with the non-dominant hand only makes the problem worse as the amount of tension on that arm will continue to be lower [2].

Different Reps

This is another common issue that might sound familiar.

You pick up one dumbbell and do bicep curls or triceps extensions with it. You aim for 8 to 10 reps to build up muscle mass but can't do as many when you grab the dumbbell with your left hand.

This difference in reps wouldn't contribute to proper form and eventually may contribute to muscle imbalances.

Injuries

And the final thing that could be contributing to arm muscle imbalances is some form of injury. This could be a muscular or tendon issue that simply doesn't allow you to work one arm as hard as the other.

Even a minor bicep injury like a tear could take ten or more weeks to repair [3].

In worse cases, it could be months and almost always ends up where one arm is bigger.

shirtless man using a dumbbell and a woman working out at the gym

Here are five unilateral exercises to get into your arm days to fix this problem.

Alternating Dumbbell Curls

These should be your go-to single-arm bicep exercises, and they are perfect for exercising at home as you need little more than a few dumbbells.

Start with your upper arms tucked in and a dumbbell in one hand. Don't alternate between the stronger and weaker arm after each rep, but complete a full set on one arm and then switch to the other.

Aim to either lift more weight or do one more set with the weak biceps. 4 sets of 8 reps is a good goal to set.

Single Arm Preacher Curls

The single-arm preacher curl is a very underrated exercise, and most people only do preacher curls with an EZ bar.

Head to the ​​preacher bench at the gym and start on your weak arm with your elbow resting on the bench in front of you.

Start with the dumbbell in your hand and the forearm in a vertical position and then slowly lower the dumbbell down for a count of 3 and then pull it back up for a count of two.

Do 4 sets of 8 reps where the last one is burning.

One thing you can do rather than switch to the other arm is to do a regular biceps curl on the stronger one.

Hammer Curls

asian man working out with a dumbbell

This is a great alternative to the preacher curl. You can do a regular biceps curl on the strong arm and then switch to the hammer curl on the weak one.

The great thing about the hammer curl is that it puts more strain on the long head of the biceps [4].

Tuck your upper arm in close to your torso and hold the dumbbell like a hammer.

Then lift for a count of two and lower back down for a count of three and do 4 sets of 8 reps.

Triceps Kickbacks

Get someone to take a picture of the backs of your arms, and you'll possibly find imbalances in the triceps as well.

Stand with one leg forward and tilt your upper body forward as well. Use an overhand grip, and your elbow tucked and upper arm parallel to your torso.

Now stretch out the arm until it's straight, and you feel the tension along the triceps. Do 4 sets of 8 reps and either less weight or fewer sets on the other arm.

You can also do this as a single-arm reverse cable curl.

Related Article: How To Get Bigger Triceps Fast

One Arm Lateral Raises

Another area where you could end up with one upper arm bigger is if you don't pay enough attention to the deltoid [5]. That's the muscle at the top of your arm that rounds out the shoulder.

To bulk this up, perform lateral raises with a dumbbell.

Hold the weight beside your body and raise your straight arm to the side until the dumbbell is shoulder height.

Then lower it down slowly.

Again, do 4 sets of 8 reps with more weight on the weaker arm.

Avoid Common Training Mistakes

woman using a pull up bar inside a gym

The biggest mistake people make is not to include enough unilateral exercises where the focus is on one arm at a time.

These are some example exercises that could cause issues:

  • Bilateral barbell curls
  • Close grip chin-ups
  • Bilateral triceps push-downs
  • Military push-ups
  • Dips

These are all great exercises, and they belong to most workout routines.

But if you focus too much on these, then you could end up compensating with the stronger arm, making things gradually worse.

FAQs

Is It Normal to Have Uneven Arms?

Yes, it is quite normal to have uneven arms. But if you don't take control of this imbalance, then things can get progressively worse over time, and that just won't give you an incredible physique.

Do Injuries Lead To Uneven Arms?

Yes, injuries can lead to uneven arms. This is especially the case where one arm may need to be completely rested and immobilized for many weeks or months, and the muscles can waste away.

Are You Ready To Fix Muscle Imbalances In Your Arms?

It's a lot more common than most people think, but dealing with arm muscle imbalances doesn't have to be a major problem.

The first thing you need to do is understand that switching to unilateral arm exercises will give you more control over the strain you put on each arm.

From there, you then add more weight or sets to the weaker side for a few months.

Depending on how significant the imbalance is, the above training routines should give you visible results after four weeks.


References: 

  1. https://www.apa.org/monitor/2009/01/brain
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6950543/
  3. https://www.mercy.com/health-care-services/orthopedics-sports-medicine-spine/specialties/shoulder-upper-arm/conditions/bicep-tear-strain
  4. https://www.shape.com/fitness/workouts/arm-workouts/dumbbell-hammer-curl
  5. https://www.physio-pedia.com/Deltoid

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