Research from the United Kingdom published in 2015 suggests that taking a hot bath can help improve running performance in hot weather, but that’s if you take the bath after exercising, not before. The study, from the University of Bangor, looked at hot baths as an alternative to other methods of acclimatizing to heat for competitive athletes. Exercising in high temperatures carries the risk of heat exhaustion, and, more seriously, heat stroke, which can be deadly. In addition, sweating to cool down in the heat puts an extra strain on the cardiovascular system and increases fatigue.
For athletes, acclimatizing to heat typically requires training for 10 to 14 days in hot weather, which can result in a drop in body temperature and an increase in sweat rate and blood plasma volume, all of which improve the ability to compete effectively. For British athletes, this may require relocating to a hot country or training in an environmental chamber simulating a hot environment, options that aren’t widely available.
Researcher Neil Walsh, a professor in the Bangor University School of Sport, Health and Exercise Sciences, explains that the hot bath recommendation stems from his own experience as a competitive road cyclist; he always took one after a long training ride.
For the Bangor study, Professor Walsh and his team recruited 17 volunteers to run for 40 minutes on a treadmill for 6 consecutive days. After each session, 10 of the volunteers took baths at 104 degrees Fahrenheit while seven others took baths at 93 degrees Fahrenheit. At first, not all the runners assigned to the hotter baths were able to remain in 104-degree water for 40 minutes, but by the fifth day, nine of them managed to stay submerged up to their necks for that long. Prof. Walsh has since said that as little as 20 minutes in the tub may be all you need, but that remains to be confirmed by further research.
All told, results of the study showed that taking a hot bath after exercise reduced both resting and exercising body temperature and improved running performance in the heat by 4.9 percent. There were no such improvements when running at cooler temperatures.
If you’re not a competitive athlete and typically avoid outdoor exercise during very hot weather, I don’t know that you need to think about acclimatizing yourself to higher-than-normal temperatures. Aside from these concerns, a hot bath after exercise – not necessarily as hot as in this study – can help ease body aches and promote relaxation.
Andrew Weil, M.D.
Mike Zurawlew et al, “Post-exercise hot water immersion induces heat acclimation and improves endurance exercise performance in the heat.” Scandinavian Journal of Medical Science and Sports, December 15, 2015, DOI: 10.1111/sms.12638