One Pec Bigger Than the Other – What to Do About It?

Bodybuilders and gym-goers don’t just aim for the leanest body fat percentage and the biggest muscles. They’re also after physical symmetry – from shoulders to quads. However, things can get very frustrating when they don’t get that sense of proportion. 

If you’re among these people and notice unevenness in your pecs, fret not because there are solutions for this! 

But first, let’s find out why the other side of your pectoral muscle is bigger than the other. Keep reading till the end as I share with you the best ways you can overcome this problem, just like I did.

What are Pectoral Muscles?

You may have heard of the pectoral muscles if you’re a gym lover. These are also sometimes called the pecs (chest muscles).

The pecs connect the upper extremities to the lateral and anterior thoracic walls or the chest bones. Their primary function is the internal rotation and adduction of the arm on the shoulder joint.

While having developed, muscular chest muscles highlight a physique form. They make your life in and out of the gym more accessible, whether pressing a loaded barbell or opening a heavy door.

Incorporating a variety of chest workouts into your routine can ensure you hit every inch of your pec muscles, maximizing your size and strength gains. 

However, engaging one side of your shoulder muscles more than the other can lead to unevenness. For instance, you do more work on your left pectoral muscle, so that side is slightly bigger than the other. 

6 Reasons Why Your One Pectoral Muscle is Bigger Than the Other

1. Dominance in One Side

One of the common reasons your one pec is bigger than the other is favoritism or dominance in one side of the body. If you perform most of your tasks on the right side, you’re more likely to develop more extensive or stronger muscles in the right chest muscles. 

The good news with this cause is you can improve it with workouts. You can often focus on your minor and significant pectoralis to remedy your uneven chest muscles.

2. Weak Mind-Muscle Connection

An essential factor determining muscle growth is the mind-muscle connection. That is why a weak mind-muscle link with your pecs may result in an overactive tricep or shoulder muscles. 

Luckily, this is something you can build with practice. We’ll discuss more of this later.

3. Genetics

One pec muscle is sometimes more significant than the other because of genetics. For instance, your right and left pecs attach to the breastbone at different points. Although you can’t alter the point of attachment, developing a sturdy and flat chest can make the difference less noticeable.

4. Medical Condition

Some medical conditions may cause an uneven chest or rib cage. These may develop over time or at birth, but surgical procedures often treat them.

Some medical conditions that may cause uneven chest development include:

  • Pectus extravatum (funnel chest) – the breastbone is sunken into the chest
  • Poland syndrome – missing muscles in one side of the body
  • Pectus arcuatum (wave-like chest) – a rare chest wall deformity
  • Scoliosis – the abnormal curvature of the spine.

If having uneven chest muscles is causing you extreme stress, it’s best to ask your doctor about it. They may suggest the proper treatment, such as surgery.

5. Bad Lifting Form

Poor form and technique cause muscle imbalances. It shifts the focus away from the prime movers, which are supposed to be your target muscles, onto the smaller synergistic muscles. 

As simple as slightly changing your movement can improve your chest muscle balance. Maybe changing the angle of your shoulder joint or elbow by a few degrees can help. Moreover, a slight change in grip may also result in a big difference.

6. How You Breathe

Poor breathing can lead to muscle imbalances. It causes weird tension in your body, and this affects your posture.

How to Fix Your Uneven Chest and Pecs

One Pec Bigger Than the Other - What to Do About It

If there’s a big difference between the shape and size of the two sides of your chest, here are the corrective actions you can take to fix the problem:

Do Unilateral Chest Press

Exercise properly to restore the balance in your body. And unilateral chest press is one of them. Keep your spine flat during the chest workout to avoid arching your lower back. 

The good thing with this workout is you’ll also lose fat, gain muscle, and burn more calories. All these benefits may help you feel and look better, improving your well-being and boosting your confidence.

Use Dumbells to Even Out the Imbalance

To balance out your dominant side, using dumbbells is a smart move. It’s a piece of gym equipment that can keep both sides of your body even, unlike barbells that allow you to cheat on your weaker side.

It’s also a good option as they are cheaper than weights. With resistance bands, you can do one arm standing neutral chest fly, one arm downward chest fly, or one arm upward chest fly. All these workouts will help you feel a great pump in your chest muscles.

Related: Dumbbell Triceps Exercises

Most Effective Chest Exercises to Remedy Your Chest Imbalance

  • One-arm push-ups
  • One-arm presses
  • Floor presses
  • Chest exercise
  • A slight incline bench workout
  • Pullovers performed with a barbell or a dumbbell
  • Dumbbell chest press
  • Dumbbell flyes

Exercise Your Weak Side

Training your less developed side more or working both sides more harmoniously is also beneficial. 

Make an effort to use your weak side (for example, your left shoulder or left pec) to lift things that can balance the muscle composition and strength on that side. 

Include your shoulders and arms on the less dominant side in your daily activities. Stretching the middle or upper trapezius muscle on the weaker pec similarly helps.

Practice Yoga

Daily hatha yoga can improve the breath capacity of the lungs, increase muscle strength, and improve the flexibility of the chest. 

If the cause of your problem is your rib cage, your physician or physical therapist may suggest yoga exercises to make your rib cage look straighter.

Improve Your Breathing

Deep breathing puts you in a good body position. Listen to your body’s feedback and make adjustments if necessary. The goal is to fill your lungs with as much air for each rep. 

Improve Mind-Muscle Connection

Focus your mental energy on the weak muscle and make it grow. One technique is to contract your lagging pectoral muscle as hard as possible. Then, hold the maximum flex to the muscle as long as you can.

Doing slower reps likewise helps. It allows you to feel your chest muscles squeezing and stretching.


One Pec Bigger Than the Other - What to Do About It

Paying attention to your physical symmetry pays off, not just for bodybuilders but for people in general. Having balanced chest muscles, for instance, will help you have a healthier and better physique. Plus, you will feel stronger because you have balanced muscles. 

With hard work and a corrected workout routine, your chest muscles will typically improve.

Hope this helps. 

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Nathan Lloyd, MSc

I’m a personal trainer, based in Boulder, Colorado.
I service clients physically in the Boulder area, mainly in the ONE Boulder Fitness Gym, but am also available for online consulting and coaching.

If you’re interested in my personal coaching programs, please contact me via the contact page.