Training in hot conditions can drive marked improvements in endurance by triggering cardiovascular and thermoregulatory adaptations. However, access to heat training chambers is limited, and the physical demands of exercising in high temperatures can be risky or impractical. A recent study found that sitting in a sauna or soaking in hot water after exercise—a practice known as “passive heat acclimation"—might offer some of the same benefits as working out in the heat, but the evidence was weak and inconsistent.

Researchers reviewed 10 studies involving nearly 200 healthy adults, comparing those who used post-exercise heat exposure via sauna or hot water immersion to those who did not. All participants completed similar exercise training programs, and the researchers analyzed outcomes related to performance in hot or neutral conditions, aerobic capacity, heart rate, body temperature, sweat response, and perceived exertion.

The analysis revealed little to no improvement in performance for those using passive heat acclimation, identifying only a 4% difference between groups—an effect that was statistically weak and inconsistent across individuals. Heat exposure slightly improved maximum oxygen uptake, sweat rate, and thermal discomfort ratings. However, the overall certainty of the evidence was low to very low, due to small study sizes and inconsistent reporting.

These findings suggest that while passive heat exposure may exert some physiological effects, its ability to improve exercise performance remains unclear. More rigorous, well-controlled trials are needed before recommending hot tubs or saunas as a reliable substitute for training in the heat. Learn more about heat exposure in this peer-reviewed article by Dr. Rhonda Patrick.