Short read
Solomon and Laye published this first meta-analysis of post-exercise heat for performance in BMC Sports Science, Medicine and Rehabilitation in 2025. The heat was either Finnish sauna or hot water immersion after training, and the two are pooled rather than analysed separately. 10 trials with 199 healthy adults, 156 men and 43 women aged 20 to 32, trained for 5 to 21 days, with 40 to 105 minutes of training a day and 14 to 40 minutes of heat per session. Every trial had a control group with the same training and no heat; Scoon 2007 and Kirby 2021 are in the pool.
Compared with the control groups, performance in the heat at 33 to 40 degrees came out around 4 % better, a ratio of 1.04 with a 95 % confidence interval of 0.94 to 1.15 and p = 0.46, which spans anything between 6 % worse and 15 % better. Under thermoneutral conditions at 18 to 24 degrees the ratio against the same controls was 1.06, around 6 %, with an interval of 0.99 to 1.12 and p = 0.08. The authors rate both as trivial. VO2max showed a small effect, Hedges g 0.33 (0.19 to 0.47); heart rate and core temperature were lower with g of minus 0.32 each, sweat rate higher with g 0.44 and perceived heat lower with g minus 0.62.
Trials were small, 6 to 20 per group, mostly men, endurance only and 5 to 21 days only. Certainty was rated low to very low throughout, owing to small samples, bias, possible publication bias and imprecision. The authors call the performance effect unresolved.
It does not show that heat after training is useless, since several physiological measures moved. The performance advantage is what remains uncertain, and sauna and hot water cannot be separated here.