Sympathetic nervous system

The sympathetic branch of the autonomic nervous system prepares the body for exertion or threat: heart rate and contractility rise, airways widen, blood is redirected to muscle, glucose and fatty acids are released, and digestion is put on hold. Adrenaline and noradrenaline are its chemical messengers.

It matters because it is not the villain of the recovery narrative. Its activation during training is exactly what should happen and is part of the adaptive stimulus. The problem is chronic activation — the state of never getting out of it, driven by sustained stress, poor sleep or excessive training load.

In practice, an elevated resting heart rate, suppressed HRV and difficulty getting to sleep after evening sessions are common signs that the balance is stuck on this side longer than it should be.