Heat Adaptation for Female Athletes
by Doug Stewart
A few weeks ago, I wrote about Racing in the Heat and strategies you can use to prepare for hot weather events. One piece of advice referenced was research linked to taking hot baths as a way to adapt and prepare for the heat. However, that piece of research was only exploring males.
A paper published at the end of last month provides a systematic review and meta-analysis exploring heat adaptation for females.
30 studies were included, with 22 in the meta-analysis, and the academics were looking to determine the impact of heat adaptation on female physiology, the effects on performance, and how different strategies impacted these factors.
Overall, it was discovered that females adapt to heat acclimatisation regimes, with lower resting and exercising body temperatures (core and skin) and lower heart rate, as well as increasing sweat rate. These results match a male population as well.
Moreover, when assessing the impact of heat adaptation on performance, those that followed the heat adaptation protocols performed better in the various tests. So it appears to be an effective strategy for performance enhancement.
However, what is particularly interesting and relevant to those looking at including heat adaptation training (training in the heat, hot baths or saunas) was that it appeared to take between 8 and 14 days/exposures to generate positive changes. Whilst the previous newsletter showed that, for male athletes, 6 hot baths seemed to result in adaptations, the papers covered in this review/analysis showed that females required more. Drilling in to some of the papers that were included in the review shows why. One paper showing minimal to no impact of heat adaptation training looked at a 5-day protocol and another paper showed that 9 days created significant differences compared to 4 days of heat adaptation training which did not have a significant impact.
Overall, it is suggested that, to achieve partial physiological gains from heat exposure, female athletes should complete up to 7 sessions of around 65 minutes each, either consecutively or non-consecutively. However, for a more complete programme to maximise physiological gains, it is proposed that a regime between 8 to 14 consecutive days of around 65 minute exposure per day should be implemented.
I think that if looking to implement then one has to be very careful an appreciate that the average duration of the sessions studied (training in the heat and passive) was 62 minutes - but with a range of 29 to 240 minutes. Additional the average number of sessions was 9, but varied from 4 to 20 sessions. For example the 29 minute protocol compared male and female runners with 3 sessions per week over 3 weeks (so 9 sessions total) with similar results for both females and males. So it may be that the 65 minutes and 8 to 14 is taking an average view of multiple approaches (e.g. training in the heat versus passive) to provide the summary and given the various papers I have read it is likely that more than 30 to 40 minutes in a passive (bath or sauna) is not going to yield greater benefits and could be detrimental.
The authors also state that:
“Finally, an exploratory meta-regression in the current review identified an association between a reduction in HR and an improvement in performance test outcomes in the heat after a heat adaptation regime. This relationship suggests that monitoring for reductions in HR during each session of a heat adaptation regime might be a useful biomarker not only for providing a measure of an athlete’s heat adaptation status prior to competing in the heat, but also indicating possible improvements in exercise performance in the heat. This finding should be taken with caution as this investigation was considered exploratory (k < 10 studies), with future research required to confirm this association and its possible practical application.”
Although further research is needed, this may allow a way of tracking progress of your heat adaptation training by monitoring heart rate.
References:
Kelly, M.K., Bowe, S.J., Jardine, W.T. et al. Heat Adaptation for Females: A Systematic Review and Meta-Analysis of Physiological Adaptations and Exercise Performance in the Heat. Sports Med (2023).