Overview
Sauna has stronger evidence than cold plunge — Finnish sauna studies show cardiovascular and mortality benefits. Cold plunge has evidence for mood and inflammation but less rigorous.
Treatment
Sauna: 15–30 minutes, 4x/week gives strongest signal. Cold plunge: 2–5 minutes at 50–59°F several times a week. Cold immediately after strength training can blunt hypertrophy — separate by hours.