Increase VO2 Max and Blood Volume? The New Science of Heat Training

Heat training causes rapid physiological adaptations by increasing blood plasma volume, which triggers the kidneys to release erythropoietin (EPO) and stimulate red blood cell production, ultimately increasing hemoglobin mass and improving oxygen transport capacity to working muscles, which can raise VO2 max by approximately 2.7 ml/kg. Research shows that both active heat training (heat suits) and passive heat training (hot tubs, saunas) can produce these adaptations, with passive methods being more accessible and less fatiguing while still providing significant benefits for endurance performance.