Short read
Kirby and colleagues at the University of Birmingham ran a controlled intervention study with 20 trained middle-distance runners, 13 women and 7 men, published in the European Journal of Applied Physiology in 2021. For three weeks, the sauna group added sessions of around 28 minutes at 101 to 108 degrees, three times a week, directly after training. A control group followed the same training programme without the sauna. The study measured heat tolerance as well as performance markers under normal temperature conditions.
After three weeks, the sauna group showed lower core and skin temperatures and a lower heart rate in a heat tolerance test. Compared with the control group, which trained identically and showed none of these changes, the sauna group reached around 8 % higher VO2max and around 4 % higher running speed at the lactate threshold. Because training was the same in both groups, the design separates the heat effect from the training effect.
The groups are still small. The sauna temperatures were very high and are not reached in many public facilities. The participants were trained athletes, so the results do not carry over to recreational exercisers.
With a mixed group in which most participants were women, the study is a more solid basis for the training context than smaller trials with men only. The gains appeared under normal temperatures, not only in the heat. What it describes is a response in trained runners under a defined protocol, not a performance gain any individual can expect.