Bigger Biceps: Enter the Rotator Cuff

Posted: October 15, 2014 by truworkout in Physique, Rehab

Arnold Biceps

Who doesn’t love reading about how to increase the size of their biceps? Countless articles have beaten me to the punch on this one, but I’ve yet to read anything on the helpful tweak I describe below. Enter the rotator cuff.

While much has been written on the rotator cuff muscles, most of that information tends to focus on shoulder pathology or its prevention, such as subacromial impingement. So why should you care about the rotator cuff and words you probably can’t pronounce if your shoulders don’t hurt and you just want bigger biceps? I’m glad you asked.

**I’ve summarized the main points in bold print for those who prefer the Cliff Notes® version.

  1. Weakness/poor muscle activation:

The shoulder and biceps muscles are intimately linked, with both having attachment points on the scapula and humerus (shoulder bones for my fellow laymen). The primary job of the rotator cuff muscles are to make sure the ball of the shoulder stays put in the socket (glenoid) when moving your arm. Imagine a mortar and pestle, only this mortar is very small and shallow and surrounded by tendons and other support structures. When the rotor cuff is weak or not functioning properly, the shoulder bone is free to smash and bump into those structures, ultimately resulting in shoulder dysfunction and/or pain. Conversely, if you are trying to keep your shoulder still while moving your elbow…such as flexing your elbow when curling, the rotator cuff must again function properly to make sure unwanted movement isn’t happening above the elbow.

Bicep Tendonitis image

The rotator cuff is supposed to prevent unwanted movement at the shoulder whether intended movement is happening or not.

Aside from rotator cuff weakness being potentially injurious, it is also less efficient. This is the part where physique enthusiasts should pay attention. If the rotator cuff is weak or not functioning well enough to properly stabilize the shoulder, less force is able to be generated through the arm to flex the elbow. In other words, you curl less weight since a larger part of your effort is wasted. To illustrate:

↑ demand for shoulder stability = ↓ force available for curling* = ↓ bicep size/strength

For any of you poor souls who have ever tried doing a dumbbell chest press on a stability ball, you will soon realize you cannot lift as much as you normally can on a regular bench, and the reasoning is quite similar. The more effort you have to spend minimizing instability, the less effort available to execute the lift…which in this case is a bicep curl.

*Arguably also due to a suboptimal length tension relationship

  1. Poor technique

In addition to the above, many lifters will excessively use other shoulder muscles such as the upper trapezius and anterior deltoids during a bicep curl*. This might be useful if you want strong anterior delts, but is certainly less than ideal for those who are out for a set of biceps with peaks at altitude. Excessive use of the upper traps, anterior delts, and low back is commonly called a cheat curl** and as the name implies, allows you to cheat by using heavier than normal weights. Cheat curling also tends to cheat your biceps out of an optimal stimulus since much of the weight is shouldered (shameless pun intended) by a combination of other muscles and momentum

*Not to be confused with intentional body English

**Observational. I have yet to see this demonstrated in an EMG study, since such a study does not exist to my knowledge.


Cheat Curl 101: Ever wonder why your lower back feels blasted after arm day??

Not everyone cheat curls or uses poor form due to being overzealous however. Sometimes it is just habit, never having taken the time to learn and practice proper form. Other times it is a compensation for muscle weakness. So again we come full circle to the first point. On top of the fact that more effort is wasted in search of stability, when a muscle is weak, other muscles must compensate to accomplish the task. It’s the way our bodies are build and for good reason. In the gym however, our body’s ability to improvise can all too often work against us.

When the rotator cuff muscles are weak, the anterior deltoids will often be quite overactive and dominant since they are used to providing additional stability to the shoulder. This means the delts are more likely to kick-in during arm movement and an exercise like…a bicep curl. In other words, rotator cuff weakness will also mean you’re more likely to cheat during a curl which equates to less bicep involvement and all the other less than ideal stuff mentioned above.

In summary, a healthy dose of dedicated rotator cuff work (stay tuned for a TRU article to come) on a consistent basis can help increase your ability to transfer force through your biceps, in other words, you’ll potentially curl more weight, the same weight more reps, and all that other good stuff. As an additional benefit, your shoulders will thank you since you will be less likely to run into impingement, tears, and other shoulder issues down the road…and if it’s results you’re after, I do hope you plan on doing this stuff for a while.

To mighty biceps,


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