Challenging the Strength Biomechanics Behind One-Arm Pull-ups

Our body is a complex machine, often raising questions that make us eager to dive deeper into the wonders of anatomy and physiology. One such intriguing question, recently put forward by Will Brownlee from our UMS Movement Mastermind group, is - if he can do six chin-ups with both arms, why can't he do three with one arm? 

In episode 338 of the Sound Of Movement  - The Unity Gym podcast we answer this question and more with the help of resident physiotherapist Phil White.

On the surface, this seems a simple query of proportionality, but the human body and its strength dynamics don't quite operate on such basic math.

Interestingly, the logic applies differently to the lower and upper extremities of our bodies. With lower limb exercises, there's more sense of crossover. 

For example, if you can do a two-legged squat with 100 kilos, it's quite possible you could perform a single-leg squat with around 60 kilos. However, this doesn't directly translate to the upper body dynamics. The disparity between two-armed chin-ups and one-armed pull-ups isn't as straightforward.

Approaching one-arm pull-up training requires a thorough understanding of the conditioning required before initiating the specific exercises. 

First, there is the bilateral pull-up, with both arms working together. This can then lead to assisted one-arm pull-ups, with the intermediate step being archer pull-ups. In an archer pull-up, you pull with one arm while the other remains straight, providing as much support as it can. To bridge the gap between regular pull-ups and archer pull-ups, you might engage in 'Eccentrics', and eventually, proceed to one-arm pull-ups.

However, rushing through this progression without first developing enough strength in the basic pull-up phase can lead to setbacks like tendinopathy. It's commonly recommended to have a one RM (Repetition Maximum) of a pull-up where you're doing 150% of your body weight before attempting one-arm pull-ups.

Consider this: an 80-kilo human, holding on with both hands, has 80 kilos dispersed evenly through two extremities. When one hand is removed from the bar, the same 80 kilos loads through only one extremity, doubling the load through one limb. This not only doubles the load but also exponentially increases the effort due to imbalance. 

The body isn't just pulling the weight in a balanced manner, but it's also fighting gravity differently and balancing itself. The muscles' motor units spread more thin, thus increasing the complexity of the exercise.

This mechanical change is more visible when you compare the upper body to the lower body. The lower body is accustomed to unilateral work – every step we take loads one leg. In contrast, the upper limbs aren't as exposed to such activities. 

Furthermore, the upper body relies heavily on the muscular control of the scapula and the balance with the arm muscles. The lack of a sturdy structure like the pelvis in the upper body makes one-arm pull-ups even more challenging.

In conclusion, the answer to why we can't do half the amount of one-arm pull-ups as two-arm chin-ups lies in the intricate interplay of biomechanics, muscular control, and the inherent difference between our body's upper and lower extremities. 

It's a testament to the fascinating complexity of the human body, providing us with endless opportunities for exploration and understanding.

You can listen to the full podcast here.