What does the all-or-nothing principle state about motor units?

The all-or-nothing principle regarding motor units states that a motor unit will either contract maximally or not at all in response to an adequate stimulus. This concept is based on the physiological properties of motor units, which consist of a motor neuron and the muscle fibers it innervates. When a motor neuron receives a sufficient level of stimulation, all the muscle fibers within that specific motor unit will contract simultaneously to their fullest potential. If the stimulus is below this threshold, the motor unit remains inactive.

This principle illustrates how nerve impulses lead to muscle contractions, emphasizing the binary nature of activation within motor units. It is important for understanding how muscles generate force and respond to varying levels of demand during physical activity.