top of page

Understanding Motor Units: Key to Effective Muscle Building

Updated: Jul 27, 2023


In the world of muscle building, you often come across the term "motor units." But what exactly are motor units, and why are they essential for muscle growth? In this blog post, we will demystify motor units and explore their role in achieving your fitness goals.

What are Motor Units?

Motor units consist of motor neurons and the muscle fibers they control. Each muscle contains several hundred motor units, though the exact number can vary depending on the muscle in question. When the central nervous system sends an electrical signal along a motor neuron, it activates the corresponding motor unit, causing all the muscle fibers governed by that motor unit to contract. This contraction leads to the exertion of force, resulting in muscle movement.

The Importance of High-Threshold Motor Units:

You might have heard the term "high-threshold motor units" being emphasised for muscle growth. Let's understand why these motor units are crucial and how to activate them.

  1. Limited Contribution of Low-Threshold Motor Units:

When you start a weightlifting session and perform a few repetitions, the low-threshold motor units are the first to be activated. These motor units control only a small number of muscle fibers, which means their contribution to muscle growth is limited. In other words, the gains achieved through low-threshold motor unit activation are relatively small.

  1. Significance of High-Threshold Motor Units:

As your workout progresses, and fatigue sets in, the high-threshold motor units come into play. Unlike low-threshold motor units, high-threshold motor units control a large number of muscle fibers. This makes them highly effective for muscle growth.

When these high-threshold motor units are recruited, they trigger a significant increase in mechanical loading on the muscle fibers. This substantial mechanical loading is essential for muscle hypertrophy and noticeable gains.

How to Activate High-Threshold Motor Units:

To maximise muscle growth, it's essential to target and activate high-threshold motor units effectively. Here's how you can do it:

  1. Lift Heavy Weights: Performing exercises with heavy resistance is one of the most effective ways to activate high-threshold motor units.

  2. Embrace Progressive Overload: Gradually increasing the weight you lift over time encourages the involvement of high-threshold motor units.


Motor units play a fundamental role in muscle building. While low-threshold motor units are limited in their contribution to muscle growth, high-threshold motor units are the key to achieving significant gains. By incorporating heavy lifting, progressive overload, and high-intensity training into your workout routine, you can effectively activate these motor units and pave the way for substantial muscle hypertrophy.

22 views0 comments


bottom of page