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Why Is One Arm Or Leg Muscle Bigger Than The Other?

Is one arm bigger than the other? Are unbalanced muscles sabotaging your workout? We’ve all wondered about this at some point, and you could be right. This is because your physicality and ability to move involves a balance of three factors relating to your muscles – the muscle’s tone, length and strength. When one of these factors falls out of line with the others, that balance is compromised. You’ll see this in the form of injuries, gait problems, and difficulties performing certain movements or progressing to heavier weights.

But how can you tell when muscle imbalance may be a problem, and what can you do about it?


What is a Muscle Imbalance?

Your bones, joints and movements are aligned by the opposing forces of muscles keeping them in place. The relationship of the muscles surrounding that joint is known as muscle balance, and when this falls out of whack, muscle imbalance causes the joint to not be able to work as it should. This can leave you with one leg, shoulder, or one arm bigger than the other.


How to Tell if You Have Any Muscle Imbalances

Muscle balance depends on the muscle’s tone, strength and length being even — not having the muscle of one leg or one arm bigger than the other. But short of suffering an injury, experiencing pain or difficulty performing a certain movement, how can you tell whether you have any muscle imbalances?

There are 3 different kinds of tests that you can try:


1. Eccentric Strength Test

Eccentric muscle contraction is the lengthening of a muscle while producing force.

You can test this by performing a simple movement that elongates a muscle. Here are a few examples:

  • Calf raises (single leg)
  • Leg extensions (single leg)
  • Tricep extensions (single arm)


2. Concentric Strength Test

Concentric muscle contraction is the shortening of muscle when producing force.

You can test this by performing simple movements that shorten a muscle. For example:

  • Single arm bicep curl
  • Leg curl, testing your hamstring


3. Isometric Strength Test

Isometric muscle contraction involves no movement at a joint. An example of this is carrying an object. The weight of it pulls you down and you oppose the weight, resisting it with equal force. Your arms don’t move while carrying the object, but your muscles contract. This is isometric muscle contraction.

There are many ways to test your isometric strength, but a few you can try without equipment at home include:

  • Plank
  • Isometric push-up
  • Hanging from a pull-up bar
  • Isometric shoulder press



What Causes a Muscle Imbalance?

We mentioned the opposing forces that are required to keep your bones centered and joints in line during a movement. When one muscle becomes tight, your joint will lean more in the direction of that tighter muscle.

Think of it this way: imagine a ball is held in place by three equal-length ropes pulling in opposite directions. When one rope is shorter (the tighter muscle) and pulled with the same amount of force as the two longer ropes, the ball will be moved more by the shorter rope. Relating this to your body, your hamstring and quadriceps keep your knee joint in place with their opposing motions, but an imbalance, such as a tight hamstring, will place greater stress on the knee cap.

You’ll normally see muscle imbalances in the front and back of your body, including your shoulders, hips and spine. They’re not always the result of an injury, and can occur from bad posture from sitting at work all day, or sleeping in an awkward position at night. It can also be caused by repeatedly performing an action over and over so that one muscle develops stronger than those opposing in the other direction. Poor technique can play a major part, too, if repeated over a long duration.

The fact is that it can also be none of the above. You may be a regular at the gym, with good sitting and sleeping posture and plenty of athletic know how, but if your training routine involves too much of one exercise and not enough of another — for example, more bench pressing than rowing — then that imbalance will ultimately show in the form of a dysfunction in your joints and movement.



How to Fix Muscle Imbalances

The good news is that muscle imbalance isn’t a life sentence. They can be corrected with exercise, effort, and repetition. Here is what you need to focus on to iron out any muscle imbalances:


1. Do more unilateral exercises

This means looking up single-arm exercises. Working out becomes a matter of habit; muscles are built and developed with repetition and resistance training, and if you’ve fallen into a pattern of one size fits all exercises, then that’s likely why you’ve now noticed a muscle imbalance.

The likes of barbell and machine exercises that use both arms will see you favor your stronger side, or place less strain on a weaker muscle — so that you end up with one arm bigger than the other. Single-limb exercises place all of your attention onto the muscles at play and can often be a good way to identify weaknesses you hadn’t realized before.


2. When training, start with the weaker side

Just about everyone has a more dominant side, and if you’re not ambidextrous then you’ll always favor one arm or one leg more than the other when performing a compound lift. The trouble with this is your stronger side will keep getting stronger and the weaker will always be slightly off balance.

A simple solution is to focus on your weaker side. Exercising it first is a good place to start while your energy levels are higher. You may also throw in an extra rep or two on your weaker arm or leg to give it the TLC it needs.



3. Focus on your form

Technique is everything and should always be your first objective. If you’re uncertain whether you’re performing an exercise correctly, consult a pro or book in for a couple of sessions with a personal trainer who will be able to show you how to do an exercise the right way. The mirrors in gyms are there for a reason and you should make the most of them to ensure your posture and technique are as they should be during a lift.


4. Do more free weight exercises

Barbells have an awful lot of great uses, as do fixed-range machines, but referring to our previous point on unilateral exercises, they may leave you a little complacent. While you might not be ignoring weaknesses or muscle imbalances, the gap between the strength of one side and another may be happening, leaving you with one leg or one arm bigger than the other. That can be fixed by hitting the free weights instead of the barbell, and finding alternative exercises that involve dumbbells in place of the bar.

Take a look at this dumbbell floor press exercise for inspiration.



Take Home Message

Muscle imbalance is the result of overworking one muscle or underworking another and, as a result, throwing a joint out of line, which will affect your strength and movement. If you don’t want to end up with one leg or one arm bigger than the other, then be aware of and work on your weaknesses. Good technique, an even workout that addresses all muscles equally, and consistency are the keys to keeping your muscles balanced.



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Jack Boardman

Jack Boardman


Jack is a fitness and nutrition writer who specialises in weightlifting, boxing and MMA training.

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