While heat acclimation (HA) protocols have traditionally lasted ~10 days, it has been suggested that short term (< 7 days) HA may provide physiological adaptations resulting in performance benefits for male athletes. However, this may not be the case for female athletes!
A recent study in moderately trained female endurance athletes examined endurance performance following a 4 and 9 day HA protocol (90 min cycling daily for 4 days or 9 days* in 40 deg C, 30% rel humidity, completed as 15 min high intensity intervals followed by 75min steady state). *Note, there was one rest day after 4 days in the 9 day HA protocol. Interestingly, performance in a hot (35°C, 30%RH) 15 min time trial was only improved after 9 days of HA, but 4 days did not seem to have the same benefits. In addition to the observed performance benefits with 9 vs 4 days of HA, sweat gland activity in the forearm was greater after 9 days of HA, and thermal comfort was improved.
However, this particular study did not control for the MC phase. While it is understood that females experience an increase in core temperature when progesterone is high (e.g. during the luteal phase of the MC or post-ovulation), experienced female athletes appear able to maintain performance in the heat by altering pacing strategies, maintaining hydration through increased fluid intake, and implementing individual cooling strategies. Thus, while females may experience greater performance challenges during exercise in the heat (and recreational athletes experiencing > challenges compared to trained female athletes), phase of MC does not necessarily influence an athlete’s ability to dissipate heat .
More research in this area is clearly necessary, but for now it appears that female athletes may benefit from a longer HA protocol (~9-10 days) compared to males. While the study referred to in this post used a heat training protocol, it is possible that using passive heat exposure (sauna, hot water bath) prior to or after training may also provide benefits without compromising the quality of training, but this remains to be studied in female athletes. At this time, strategies to help with heat acclimation in females should be individualized for the athlete.
PMID: 34116919; 34127636; 31891914; 33123618; 31156449, 31555140, 30377639