Biofeedback

Biofeedback is a training technique in which a person watches real-time signals from their own body — heart rate, HRV, EEG, breathing, skin conductance — and uses that feedback to consciously train control over otherwise involuntary processes.

The most-studied form is HRV biofeedback, in which a user breathes at a specific resonant frequency while watching their heart rate variability change. Over weeks of practice, the trained pattern becomes easier to enter on demand and produces measurable changes in autonomic regulation.

Biofeedback has been around for decades and has a real research base, particularly for stress, anxiety, and chronic pain. It's one of the older and better-validated forms of consumer-accessible nervous system training.