Central nervous systemCNS

The central nervous system comprises the brain and spinal cord. It integrates incoming sensory information and issues the motor commands that travel out through the peripheral nerves to muscle.

It matters to training because much of what improves in the early weeks is central rather than muscular: better recruitment, better coordination, less inhibition. It is also the reason skill practice transfers so specifically — you get better at the movement you actually rehearse.

In practice, the popular concept of 'CNS fatigue' from heavy lifting is used far more loosely than the evidence supports. Measurable central fatigue exists but is modest and short-lived after typical strength sessions; most of what people attribute to it is peripheral fatigue, poor sleep or accumulated life stress.