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Right Arm Bigger Than Left

Right Arm Bigger Than Left (How to Fix Muscle Imbalances)

One of the greatest frustrations for anyone that frequently lifts weights is when you realize you’ve developed a muscle imbalance. This can be even more noticeable and frustrating when you realize that one arm is bigger than the other (usually it’s your right arm bigger than left as this is more people’s dominant hand).

What should you do though when you have a right arm bigger than left or one arm is bigger than the other?

A right arm bigger than left is a common muscle imbalance that is usually the result of favoring your dominant arm for everyday tasks and having a more efficient motor unit recruitment through weight training. To reduce this, use unilateral training and a consistent rep range to reduce this imbalance. 

Having a dominant arm is not the only cause of a muscle imbalance though and adding more sets is not the best solution to fixing this imbalance. In this article, I’ll cover why you have one arm bigger than the other but more importantly, how to fix it.  

Right Arm Bigger Than Left?

Usually, when you’ve been working out for a number of months and years you’ll naturally start to build a noticeable amount of muscle mass. When this happens, you might also notice that you have one arm bigger than the other. 

The first thing you need to do when you notice this is not to make an assumption. Our muscles create an illusion based on the angles from which you view them. One of the keys to bodybuilding posing is to display your physique optimally but manipulating your posing angles. 

The more practical thing you should do is pull out a tape measure and measure both arms relaxed and also flexed. You should measure from the largest area which will be your mid-arm when relaxed and from the top of your bicep “peak” when flexing. 

*** If you are unsure then check out this link or watch the video below.

Once you have an accurate measurement, you’ll know whether or not you were just imagining a difference in arm size or if you have a genuine muscle imbalance. 

Is It Normal to Have One Arm Bigger Than the Other

According to research, 85-90% of the earth’s population is right handed. What this means is that we have a dominant hand that takes preference and priority when performing certain tasks. We are not sure why this has developed but the fact is, most of us have a dominant hand and that hand is the right one. 

As a result of having a dominant hand, you’ll find that you do a significant amount of tasks with one hand in comparison to the other. 

  • Brushing your teeth
  • Writing
  • Texting
  • Eating
  • Throwing
  • Catching 
  • Carrying shopping

The list is quite endless and if you take a moment to think about your everyday actions, you’ll soon realize you have a preference. Even reaching for a coffee I’m aware that I’m doing so with my right hand as I write this. 

This use of repetition over time means that your dominant arm becomes more developed. The use of fine motor skills and repetitive actions will lead to a slightly more developed arm and this means it is normal to have one arm bigger than the other. 

This arm, however, should not be noticeably different in size and this is where an imbalance can be the result of training. 

What Causes One Arm to Be Bigger Than the Other

The cause of one arm being bigger than the other is not necessarily just using one arm more frequently for everyday tasks. Brushing your teeth with just your right hand will not suddenly make the bicep and tricep on this arm freakishly disproportional. There are some other factors at play…

1. Muscle Dominance

By muscle dominance, what I really mean is that you likely have a dominant hand/arm. Most people do unless you are in the rare minority of ambidextrous individuals. 

I’ve just covered this above but what this means is that even when lifting weights, one arm is more likely to take over and do more of the work. This isn’t even something you control through though but an almost involuntary action as a result of muscle memory. 

If you do something with your right hand all of the time, that acts as a signal to your body as you build connections through your nervous system to be more efficient. Having an overly dominant hand can therefore be one of the main reasons why one arm is bigger than the other. 

2. Muscle Fiber Proportions

Secondly, your muscle fiber proportions might be slightly different between your two arms. What this means is that a higher proportion of fast-twitch fibers in one arm (even by as little as a 1% difference) can over time result in more muscle growth as fast-twitch fibers are more responsive to growth. 

One arm might also be better at recruiting motor units (usually the dominant hand) and this means that the same movement will result in the arm that can recruit more motor units (muscle fibers) receives more stimulation which leads to more growth. 

The margins for this are small but it can still be a factor. 

3. Genetics

Finally, genetics play a part. The human body is not symmetrical and while the aim for bodybuilders is to develop a truly symmetrical physique, only the top-level athletes make it to this position because of genetics. 

My abs, for example, are asymmetrical. The left side of my abs is positioned higher up than the right side and this will not change through training as it’s a genetic factor. Muscle bellies and proportions can commonly be different between two sides of the body and the shape of a muscle can also dictate its size.

Your muscle imbalance could therefore be genetic and while training can help reduce the imbalance, this isn’t something you can always achieve as you can’t shape a muscle, it can only grow or shrink based on its insertions points and shape.  

How to Fix One Arm Bigger Than the Other

Fixing a muscle imbalance is not necessarily easy, though it is very achievable if you follow some simple steps that I’ll list below. 

1. Use Unilateral Exercises

The best thing you can do to reduce and fix a muscle imbalance for your arms is to use more unilateral exercises. This means that each arm will work independently from the other one. Take the barbell bench press for example.

With a fixed bar that is controlled by both arms, it can be easy for a dominant arm to take over and essentially lift more of the weight. If however, you swap a barbell with dumbbells, both arms will now be equally responsible for lifting the exact same amount of weight. 

The dominant arm can no longer help the non-dominant arm and therefore all reps and sets will create equal stimulation between both arms. 

This can be applied to multiple exercises for shoulders, back, chest, and arms. I’d only caution that in some exercises, it’s still fine to use a fixed bar but introducing more unilateral exercises will help to balance out the training stimulation and reduce the muscle imbalances. 

Unilateral work is perhaps the most beneficial way to reduce a muscle imbalance and this should be the first thing you start to implement. 

2. Consistent Reps

This one is usually more of a preventative measure but it’s something I frequently see with younger lifters not necessarily following a set rep scheme and that is an imbalance in terms of reps. 

Let’s say you are doing alternating dumbbell curls and your rep target is 8 reps with each arm. Your dominant arm is likely going to hit this target comfortably depending on your weight selection but often, you’ll find the dominant arm fails a few reps early at 6-7 reps. 

The reason I mention younger lifters is that they will push each arm to failure on a set even though the failure points for both arms could be different. If you can only hit 6 reps with your left arm but manage to do 12 with your right, there’s a very good chance that your right arm is not only going to be bigger already but that the more stimulation it’s receiving could make it grow further. 

To help fix one arm being bigger than the other, make sure you use the same number of reps for each body part regardless of what the failure point is. Over time, this will allow the smaller arm to catch up in terms of strength and size to the larger one. 

3. Increased Training Frequency

If you are following the first two steps above then this point should only be considered as a last resort in examples of extreme muscle imbalances. Increasing training frequency involves training the non-dominant arm with a higher frequency than the dominant arm. 

If you train arms for 16 sets per week split over two training days, the secret to reducing the muscle imbalance is not to add more sets to these sessions to stimulate more growth. If this was the case, you’d simply add more sets for all body parts to experience unlimited growth!

This is an approach you’ll see many people take to try and fix a muscle imbalance (so much so that people often ask can you train arms everyday) but instead, you should increase the training frequency for your non-dominant arm. This could be as simple as adding an extra 3 sets to a rest day. 

The reason why this is a better approach is that the stimulation will activate muscle protein synthesis (MPS). This is a muscle-building state brought about by both resistance training and protein consumption that can last anywhere from 24 – 72 hours depending on how training the individual is. 

By activating this more frequently with some additional sets for your non-dominant arm, you can activate more muscle growth without impacting your central nervous system through additional training sessions.  

Final Thoughts

Having a right arm bigger than left or vice-versa can be a big frustration for many people, especially if it’s noticeably different in size. The first thing to do though is to get out the measuring tape and check for sure as sometimes this can all be in your mind and you see an imbalance that isn’t actually there. 

If you do have a muscle imbalance with one arm bigger than the other then this is something you can fix. Start to utilize unilateral training and ensure that all reps you do are equal, one arm should not do more work even if it has the capacity to do so. 

Finally, you can even add in some increased frequency to try and stimulate more growth but this method is by no means a guarantee. Applying these principles though should go a long way towards reducing and potentially even eliminating a muscle imbalance between your arms.

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