The size principle of motor neuron

The size principle of motor neuron recruitment• The smallest motor neuron is recruited first and the largest motor neuron last • The size principle has two important consequences for the control of movement by the nervous system.• First, the sequence of motor-neuron recruitment is determined by spinal mechanisms and not by higher regions of the nervous system. This means that the brain cannot selectively activate specific motor units. • Second, motor units are activated in order of increasing fatigability, so the least fatigable motor units available produce the initial force required for a specific task.