One Arm Bigger Than The Other? Do These 7 Things To Fix

fix one arm bigger than the other

If you have noticed that one of your arms is more muscular than the other, you may be asking yourself if this is something to be concerned about (or, at the very least, it is normal).

Having one arm more muscular than the other is typically a harmless issue. It generally occurs because your dominant arm is used more often than the other. However, you can address this imbalance by adding more dumbbell exercises and paying closer attention to your weaker arm during workouts.

To help you build better muscle symmetry and minimize strength imbalances in your arms, I’ll dive into the top reasons why this has occurred and how to address each of them. 

I will also share a sample 2-day biceps and triceps workout that you can do to improve the size and strength symmetry between your arms.

Related Article: 27 Best Arm Exercises for All Levels

If your arm size and upper body strength are something you are struggling with, let Fitbod help. On average, a new Fitbod user who trains 3 times a week for about 45 minutes will see a 34% strength increase after 3 months. Try Fitbod for free.

Is It Normal To Have One Arm Bigger Than The Other?

It is normal to have one arm bigger than the other to a certain extent; however, drastic differences in function or aesthetics can be challenging, so you can train to address muscle and strength imbalances to minimize them as best as possible.

Many people have expressed that they have one arm bigger than the other and they’re wondering if it’s normal:

“My right arm is bigger than my left arm. Should I stop lifting with my right arm until the 2 are the same size?” – Quora User

“My left upper arm is bigger than my right upper arm. Is that normal? How can I fix that?” – Quora User

“My left bicep is larger than my right, but my right is fairly stronger. How do I get them to equal size and strength?” – Quora User

As you can see, this is a prevalent issue but it isn’t necessarily a problem. There is no established range of imbalance that you should try to shoot for, however, your primary focus should be to minimize any strength imbalances. After that, you can start to address size imbalances. 

A general recommendation is to keep your muscle size imbalances under 3-5%.

For example, if you have one arm measuring 15” and there is more than a .75” difference between that arm and your other arm, then this may be an issue. 

Related Article: 11 Compound Arm Exercises for More Arm Strength and Size


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Reasons Why One Arm Is Bigger Than The Other

reasons why one arm is bigger than the other

Before we dive into ways to address the issue, it’s important to understand WHY this happens in the first place. The main reasons are:

Dominant vs. Non-Dominant Arm

Everyone has a dominant arm that they do most activities of daily life. Those non-exercise activities can add up, whether this is carrying a bag or holding a child. 

While this is something you should not be overly concerned with, you can balance out the work your arms are doing by being more conscious of any activities you could do with your weaker arm.

Poor Form During Training

People who train primarily with machines and barbells are more prone to muscular imbalances because their stronger arm can take over to lift more of the load (rather than a 50/50 effort by both sides). 

The stronger arm will want to take over when fatigue sets in and you start to struggle, so be hyper-vigilant about maintaining your technique throughout the entire set to avoid shifting the load to the dominant side.

Lack of Emphasis on Unilateral Arm Training

If your upper body exercises are all bilateral (both arms working together) exercises using machines, barbells, and cable attachments that don’t allow your arms to work independently then you will probably have one arm bigger than the other.

A lack of unilateral (one side at a time) training can cause arm imbalances if you’re shifting the load to your dominant side (as discussed above) and fail to address imbalances that already exist. 

When training with dumbbells or cables (single-arm movements), strength imbalances become very apparent as your weaker side is unable to keep up with your stronger side.

Prior Injuries

Prior injuries can drastically influence the size and strength of your arms as well as your movement patterns. 

If you have any pain or discomfort during training, it will be a natural response to shift loading to other muscles (the more muscular arm) to lift the load.

Even if your prior injury isn’t painful anymore, you may be so accustomed to compensating for the injury that you’ve developed movement patterns that shift the emphasis off of the previously injured arm.

Lastly, if you were unable to train the injured arm for quite some time, you may have developed an imbalance from lack of use and have yet to regain the strength and size of the weaker arm.

Common injuries that would affect symmetry are sprains, strains, fractures, or connective tissue injuries (i.e. tendinitis) of the wrists, elbows, triceps, biceps, and shoulder girdle. 

Related Article: 15 Best Dumbbell Arm Exercises for More Muscular Arms

7 Things To Do If One Arm Is Bigger Than The Other

things to do if one arm is bigger

Below are seven things you can do to address size differences between your arms.

1. Pay Attention to Your Form

When doing arm exercises that train both arms simultaneously, you must focus on slowing the movement and loading both arms evenly. 

As you approach the point where fatigue starts to set in, make sure you are focusing on your weaker/less muscular arm so that you maintain your technique and avoid shifting the weight to your dominant arm.

Having a partner there to correct you or video your form for feedback can help to ensure you maintain proper form throughout the entire set (especially with barbell movements).

2. Include More Dumbbell Movements

If you do not train with dumbbells or only use them a few times a week, try spending 6-8 weeks with dumbbells as the main equipment you use to build your arms. 

Dumbbells will force your arms to get stronger and grow equally, as you cannot use your stronger arm to compensate for a weaker arm. This is the main benefit of dumbbells, which goes beyond just arm training (you can do this for back, chest, and shoulder training as well).

3. Train Single-Arm Movements First

By training one-arm movements first, you can train each arm equally when they are both at their freshest state. This will help you build strength in both arms and discourage the more muscular arm from taking over early in the session.

Changing the order of your movements to place single-arm movements first can also help establish a better mind-muscle connection so that you can feel both sides working equally.

4. Train Your Weaker Arm First

When performing single-arm movements, start by training your weaker arm first. This will ensure you get good quality reps on the weak arm first when you are the most fresh. 

You may still be able to get more reps afterward on the stronger arm, but it’s better to train the weaker arm before fatigue sets in than to be fatigued when training the weaker arm.

You should train your weaker arm first every time you do dumbbell rows, one-arm curls, tricep kickbacks, or any other exercise where you would generally pick up the load with your dominant hand first.

5. Add Another Set to Your Weaker Arm

Adding an extra work set is a great way to increase volume for your weaker arm without overdoing it. By adding an additional set (i.e. doing 4 sets of curls on the weak arm and 3 on the more muscular arm), you will see the size and strength gap decrease.

You don’t need to do this for all exercises, as this can be excessive. Start by choosing 1-2 movements for each arm session (one for the biceps and 1 for the triceps) and focus on adding an extra set for your weaker arm. 

Refer to the sample program below to better understand how to do this in your own programs. 

6. Do a Few More Reps on Your Weaker Arm

Another way to add extra volume to your weaker arm is to add a few more reps. This is particularly helpful if you are unable to commit to another set due to time restrictions or fatigue.

If you are struggling to perform more reps on your weaker arm because your muscles give out before you can do so, you can try implementing a quick rest-pause set. 

This means you break down a larger set into two or even three smaller sets, with very short rest periods (under 10 seconds) to drive muscle growth and train past failure. 

Once you cannot do any more reps on your weaker arm, break for 5-10 seconds and get a few more reps. Repeat this until you do 10-20% more reps on the weaker arm than the more muscular one.

7. Go Heavier on Your Weaker Arm

Until this point, we talked about how to increase overall training volume through increasing sets and reps, which is a great way to address any size differences you may have between arms.

However, if there is a significant strength difference between your arms then it may be more important initially to add in some heavier training on the weaker/smaller arm rather than focusing solely on additional training volume.

Going heavier with the weaker arm can help decrease the strength gap between your arms to ensure their functionality is more similar.

For example, let’s say you are doing one-arm dumbbell curls, and you can do 12 reps with 35 lbs on your stronger arm and, even when trained first, your weaker arm can only perform 9 reps with the same load. 

Instead of doing a rest-pause set to get yourself to 12-15 total reps, you could try to lift 40 lbs with your weaker arm for 5-8 reps, and then drop to 30-35lbs to get the remaining reps to match the stronger arm’s rep count.


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Sample Training Program For Arm Symmetry

sample training program for arm symmetry

To help you implement the strategies listed above, I’ve created a 2-day arm training program that addresses muscle imbalances in both the biceps and triceps. The first day focuses more on the biceps, and the second is more on the triceps. 

You will notice that both days still include movements that train both arms simultaneously, this is because these exercises help to build overall strength. However, you want to ensure you consciously load both arms evenly as you lower and lift the weight. For this reason, strict tempos (3-4 second lowering phases) are being used.

When training the single-arm exercises (dumbbells or cables), train the weaker arm first, then the more muscular arm. A few of the exercises also have you adding another set to the weaker arm (and not the more muscular arm); these exercises are denoted by an “*”.

All exercises can be found in the Fitbod app; the exact workouts are not. You can use the below sample training program as a 4-6 week workout template to build your own within the Fitbod app.

Day 1

  • Barbell Curl: 4 sets of 8 reps, 3-second lowering, 1-sec pause on in the bottom
  • * Dumbbell Incline Curl: 4 sets of 8 reps
  • Smith Machine Skullcrusher: 4 sets of 12 reps, 3-second lowering, 1-sec pause on in the bottom
  • * Dumbbell Floor Press: 4 sets of 12 reps

Day 2

  • Close Grip Bench Press: 4 sets of 8 reps, 3-second lowering, 1-sec pause on chest
  • * Cable Triceps Pushdown: 4 sets of 8 reps
  • Concentration Curl: 4 sets of 12 reps, 3-second lowering, 1-sec pause on in the bottom
  • * Incline Hammer Curl: 4 sets of 12 reps

About The Author

Mike Dewar

Mike holds a Master’s in Exercise Physiology and a Bachelor’s in Exercise Science. He’s a Certified Strength and Conditioning Specialist (CSCS), USA Weightlifting Advanced Coach, and has over 10+ years of experience working with collegiate athletes, national level lifters, and beginners alike. Mike is Founder of J2FIT Strength and Conditioning, a growing global training company with gyms in New York City, Cincinnati, and online offering personal training, online custom coaching programs.