How does the body recruit motor units during muscle contraction?

The body recruits motor units according to the intensity of the contraction required, a principle known as the size principle. When a muscle needs to exert more force, the nervous system systematically activates more motor units and begins with the smaller, less powerful ones before moving on to larger, more powerful motor units. This orderly recruitment allows for smooth and controlled increases in muscle tension.

For example, during light activities, only a few motor units are activated, which suffices for minimal force generation. As the force requirement increases, more motor units are engaged to meet the demand efficiently. This selective recruitment ensures optimal performance while minimizing muscle fatigue. The concept is essential for understanding how the body adapts to varying physical activities and intensities, ensuring that muscle contractions are efficient and controlled.