Breathwork (respiratory training) increases athletic performance

Soccer players showed the most promising results—those doing respiratory training covered about 115 meters more distance in fitness tests and improved oxygen uptake by approximately 1.6 mL/kg/min. However, swimmers and cyclists showed no significant improvements, and most measurements of lung function improvements were modest.

Limitations: 1) athletes and trainers knew who was doing the real training vs. fake training, creating placebo bias; 2) most individual studies were small (under 20 people per group), making results unreliable; 4) the benefits seem highly sport-specific rather than universal.