One Bicep Bigger Than The Other? Muscular Imbalances Explained

published by: Debbie Luna
Last Updated:
May 24, 2022

Among the various aesthetically pleasing muscles is the ever popular biceps brachii - a two headed skeletal muscle group that attaches to the radius of the forearms and originates from the scapula, making it responsible for forearm supination and flexion.

However, many exercisers may notice that one biceps brachii is noticeably bigger than its counterpart on the opposite arm, presenting an unpleasing visual asymmetry and bringing to mind concerns about injury development.

Fortunately, it is rather common for individuals to possess one biceps muscle that is larger than the other; an issue that is also quite easy to remedy, with only subtle changes in their workout programming being needed to do so.

Why Can One Bicep be Bigger than the Other?

One muscle group being larger than its counterpart on the other sagittal plane of the body is not solely reserved for the biceps brachii, as such issues may develop in practically any skeletal muscle group that receives uneven training stimulus.

This is referred to as a muscular imbalance, and is luckily not permanent and not very dangerous in the case of uneven biceps brachii.

biceps brachi muscles

Muscular imbalances do not solely apply to the relative size of the muscle itself, but also to the proportional strength output it is capable of producing - with smaller muscle groups on one side usually also being weaker than the larger muscle group on the opposite side of the body.

The particular reasons why an exerciser would develop a muscular balance may be difficult to pin down; but usually revolve around their training methodology, what sort of exercises are involved in said training, or even due to a factor entirely unrelated to exercise that can otherwise produce muscular hypertrophy in the muscle group.

What Causes Muscular Imbalances?

Muscular imbalances primarily develop due to uneven resistance training stimulus being placed on a muscle group over long periods of time.

In the case of uneven biceps, this is usually due to barbell based bilateral isolation movements that allow one arm (usually the dominant one) to overpower the other and bear a larger portion of the exercise’s resistance.

Exercises such as chin-ups, barbell rows, and barbell curls in particular are the usual culprits behind one bicep being bigger than the other on an exerciser’s body.

Even in instances where the exerciser’s uneven biceps are not caused by overuse of bilateral movement, form discrepancies such as one side of the body achieving a fuller range of motion or longer time under tension during resistance exercise may also result in such an asymmetry.

Other cases of training induced biceps asymmetry may be due to a history of injury impacting the hypertrophy of one bicep, or the repetitive usage of mixed hand grip form during certain exercises such as the rack pull or deadlift.

Can Uneven Biceps Develop for Reasons Unrelated to Training?

Certain habits or simple facts of life can lead to a natural asymmetry in an individual’s biceps size and strength, such as would be the case in individuals who work a labor intensive job that may induce muscular adaptations in one bicep more than the other.

Other factors unrelated to resistance training that can otherwise result in uneven biceps are that of natural hand dominance leading to greater blood flow and stimulus response in one bicep, or simple genetic predisposition to such an asymmetry.

Who Usually Develops Muscular Imbalances?

More often than not, it is usually novice exercisers or athletes returning to training after a long period of inactivity that develop muscular imbalances such as biceps brachii asymmetry.

This is not only due to the accelerated rate at which these individuals develop their musculature, but also because they have yet to fully master (or re-master) the mechanics, form cues and bodily coordination required to properly develop symmetrical biceps, especially in the case of novice exercisers utilizing compound movement based training routines.

However, there are a few cases of more seasoned exercisers developing uneven biceps, either due to consistent usage of incorrect form or overreliance on unilateral biceps isolation movements such as the EZ bar curl or preacher curl machine.

Regardless of whether the individual with asymmetric biceps is a newbie to the gym or an advanced weightlifter, remedying the muscular imbalance simply requires an alteration in their training programming.

Are Uneven Biceps Dangerous?

For the most part, unless the uneven biceps are a sign of a deeper injury - asymmetric biceps are of no concern in regards to safety or health, and are more an issue of aesthetics or personal preference.

The rare instance where uneven biceps may place an exerciser at risk of injury would be if the exerciser were to attempt a unilateral biceps based movement that proves too strenuous for the weaker or smaller biceps muscle, potentially injuring it.

This, however, is uncommon so long as the exerciser adheres to proper form and the usage of a reasonable amount of weight for their particular exercise - and as such is usually not a cause for concern.

Common Mistakes in Training that Lead to Uneven Biceps

Though having one bicep bigger than the other is not usually a cause for concern, exercisers wishing to prevent it from occurring or to remedy such an issue must examine their training methodology and workout programming.

Earlier in this article, we have gone over certain factors that contribute to the development of skeletal muscle asymmetry - but just barely touched upon specific training mistakes that directly cause uneven biceps, such as the usage of a mixed hand grip form or excessive unilateral volume that worsens the asymmetry.

Over Reliance on Unilateral Movements

Having one bicep bigger than the other does not occur instantaneously - or solely due to training, as certain lifestyle factors can lead to an exerciser having a more dominant bicep in terms of strength and size.

This, when combined with unilateral exercises that recruit both biceps brachii in a simultaneous manner, will result in the asymmetry worsening even further as the two muscles develop at a consistent rate.

While unilateral exercises - unilateral biceps isolation exercises in particular - can indeed cause one bicep to be bigger than the other, they may also cause this muscle asymmetry to become more pronounced, a common error made by lifters mistakenly attempting to correct their uneven biceps through resistance exercises.

Frequent Usage of Mixed Hand Grip

An issue that is more specific to pulling motion exercises such as the cable row, deadlift or rack pull, the usage of a mixed hand grip wherein one hand is supinated while the other is pronated will often directly cause muscular imbalances to occur not only in the biceps but throughout the entire body.

mixed grip

This does not necessarily mean that the usage of a mixed hand grip is inadvisable however, as the exerciser simply must ensure that both arms are receiving an equal amount of training stimulus in a similar manner by switching their hand grip between repetitions.

It is also important for the exerciser to keep in mind that only repetitive long-term usage of a mixed hand grip will result in asymmetric biceps, as one or two sets performed with a mixed hand grip will not induce enough muscular hypertrophy to result in such an imbalance.

Improper Form and Asymmetrical Load Distribution

Another common mistake that results in one bicep being bigger than the other is the usage of improper form or asymmetrical load distribution during an exercise - with such habits like utilizing a larger range of motion with one arm, moving one side of the body first in a unilateral exercise or spacing the hands unevenly along a barbell all altering the distribution of training stimulus between the biceps.

This is easily fixed by simply ensuring that the exerciser pays attention to form cues and retains proper exercise mechanics - especially in the case of improper form, which not only will cause uneven biceps, but potential injury.

How to Fix Biceps Asymmetry

Fixing biceps asymmetry is rather simple - all that is required is switching out any bilateral exercises that recruit the biceps brachii with an alternative unilateral exercise.

This will force the biceps to work independently of one another, resulting in an equal amount of training stimulus that will allow the smaller bicep to “catch up” with the larger bicep in terms of muscular development and strength output.

A caveat to this is that the exerciser must ensure that the weaker or smaller bicep dictates the volume and resistance of the exercise - that is to say, when the weaker bicep becomes fatigued, the exerciser must end the set so as to provide a larger training stimulus in comparison.

In the case of a training routine that does not allow for unilateral exercises to replace bilateral exercises (such as in certain powerlifting programs), adding extra unilateral biceps isolation exercises to the end of the workout session can also provide an effective solution to one bicep being bigger than the other.

References

1. Burdukiewicz A, Pietraszewska J, Andrzejewska J, Chromik K, Stachoń A. Asymmetry of Musculature and Hand Grip Strength in Bodybuilders and Martial Artists. Int J Environ Res Public Health. 2020 Jun 30;17(13):4695. doi: 10.3390/ijerph17134695. PMID: 32629826; PMCID: PMC7370066.

2. Sterkowicz S, Jaworski J, Lech G, Pałka T, Sterkowicz-Przybycień K, Bujas P, Pięta P, Mościński Z. Effect of Acute Effort on Isometric Strength and Body Balance: Trained vs. Untrained Paradigm. PLoS One. 2016 May 24;11(5):e0155985. doi: 10.1371/journal.pone.0155985. PMID: 27218258; PMCID: PMC4878781.

Debbie (Deb) started powerlifting and Olympic lifting in High School as part of her track team's programming; She continues to train in order to remain athletic. Inspire US allows Deb to share information related to training, lifting, biomechanics, and more.
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