Spring in the northern hemisphere is upon us. The spring also brings a busy race season filled with marathons, ultramarathons, and multisport events. Inevitably, some of these races will experience much warmer weather than expected. This can not only slow athletes down in spring races but can also increase the risk of experiencing a heat related illness. If you are racing in the spring or early summer, here are 3 things you need to know about heat acclimation:
Heat acclimation happens within 10 – 14 days, but you start to lose it within 24 – 48 hours!
If you exercise in the heat every day, your body will acclimate to the heat within 10 – 14 days. This can be accomplished either by exercising at low intensity (< 50% VO2 max) for long duration (60 – 100 minutes), or by exercising at moderate intensity (75% VO2 max) for short duration (30 – 35 minutes). The changes in your body that take place with heat acclimation are:
Increased capacity to sweat and therefore cool your body (Houmard et al, 1990)
Reduced salt loss in your sweat (Houmard et al, 1990)
Reduced body temperature at similar exercise intensity (Buskirk & Bass, 1974)
Reduced heart rate at similar exercise intensity (Buskirk & Bass, 1974)
However, it is important to note that for every day without heat exposure, you lose approximately 2.5% of the core temperature and heart rate adaptations per day (Danaan et al, 2018).
If you are not heat acclimated, you must adjust your pacing plan.
Safety first! Don’t be stubborn with this one. Be willing to adjust your pacing plan if the weather is unusually warm and you are not yet heat acclimated. Below is a table with data from the Jack Daniels tables and the impact of various temperatures on a 4-hour marathon pace.
The impact of temperature on marathon time
Use sauna training as a heat acclimation strategy
Often times, it is not feasible to train in hot conditions leading up to a race. For example, if you are training for the Western States 100 in June but live in Minnesota, you will not be training in similar environmental conditions as the race. This is an example where sauna training can aid in an athlete’s heat training in the lead up to the race. Below is a sample sauna training protocol based on Kirby et al 2021.
It’s important to note that research studies use quite a long sauna time (30 minutes) as they need to set up a protocol that will likely induce physiological results. As a personal experiment, you could try shorter durations to see how you feel.
An example of a sauna protocol for endurance athletes.
References:
Buskirk ER & Bass DE (1974). Climate and Exercise. In Science and Medicine of Exercise and Sport, ed. Johnson WR and Buskirk ER, 190 – 205. New York: Harper & Row.
Daanen, H. A., Racinais, S., & Périard, J. D. (2018). Heat acclimation decay and re-induction: a systematic review and meta-analysis. Sports Medicine, 48, 409-430.
Houmard JA et al (1990). The influence of exercise intensity on heat acclimation in trained subjects. Medicine and Science in Sports & Exercise, 22: 615-20.
Kirby, N.V., Lucas, S.J.E., Armstrong, O.J. et al. Intermittent post-exercise sauna bathing improves markers of exercise capacity in hot and temperate conditions in trained middle-distance runners. Eur J Appl Physiol 121, 621–635 (2021). https://doi.org/10.1007/s00421-020-04541-z