Size principle of motor unit recruitment

Skeletal muscle fibers are grouped into motor units, each of which is innervated by a single motor neuron. This means that muscle contractions are generated and modulated by activating differing numbers of motor units. Because various motor units have specific thresholds of activity, a muscle contraction develops by stimulating motor units sequentially, from slowest and weakest to fastest and strongest. While slow type one fiber motor units are active during essentially all muscle contractions, high threshold fast twitch motor units are only incorporated during moderate and maximal efforts.

[@uzaykanberoglu]

This helped me understand the concept easier, thanks Professor!

[@mechanismsandlogicinhumanp5840]

Glad it helped!

[@tiegodiniz4201]

Which reference this did come?

[@mechanismsandlogicinhumanp5840]

The original was Henneman's paper in 1957. There have been quite a few more related references since then as you can imagine.
Henneman, E. (1957). Relation between Size of Neurons and Their Susceptibility to Discharge. Science, 126(3287), 1345-1347