Motor Unit Recruitment,

Alright, let’s dive into this analogy to understand the fascinating concept of Motor Unit Recruitment, which is actually a very important step to learn, when trying to understand hypertrophy. And as Henneman’s size principle suggests — Motor Units are usually recruited in order, from smaler to largest, depending on the force they need to exert, contraction velocity and perceived effort levels.

Imagine that you and your friends are pushing a car uphill. You and your friends represent motor units, while the car is is the “load” or “force” that your muscles need to generate.

If the car is a small, lightweight vehicle, perhaps a compact car, not everyone will have to push the car uphill immediately. One or two friends (representing the smaller motor units) could start pushing it.

These “smaller motor units” have more endurance and can keep working for a long time, allowing the others to rest. This is like when you’re performing an exercise with light weights, and only some of your motor units are required.

On the other hand, if the car is a heavy-duty vehicle like an SUV or a truck, all your friends will need to push from the start. The steep hill (increased load) requires maximum effort right away. This scenario is similar to lifting heavy weights where all motor units, including the larger ones, need to be recruited immediately to generate the necessary force.

But what if the light car is carried for a long time?

In that case, as your friends start to get tired, they’ll need help from the others to keep the car moving uphill. This is analogous to more motor units being recruited to sustain the effort as fatigue sets in during an exercise!

So, in this analogy, the process of getting more friends to help push the car as it becomes more difficult or as they become fatigued is equivalent to motor unit recruitment. This principle attempts at demonstrating how your body adjusts to different levels of physical stress to optimizes its resources and exert force as efficiently as possible!