Box breathing (also called square breathing or four-square breathing) is a simple breath regulation technique used by U.S. Navy SEALs, first responders, and athletes to regulate the nervous system under stress. The technique involves four equal phases: inhale for 4 counts, hold for 4 counts, exhale for 4 counts, hold for 4 counts — creating a 'box' shape. This controlled breathing pattern activates the parasympathetic nervous system and reduces cortisol, heart rate, and the subjective experience of stress within minutes. It requires no instruction or equipment and can be practiced anywhere, making it one of the most practical and accessible stress management tools available.

Reference:

Wikipedia: Pranayama (Breath Regulation)

https://en.wikipedia.org/wiki/Pranayama