Most runners are aware that when summer rolls around, their body needs to acclimate to the rising environmental temperature. The human body will respond to a couple weeks of running in the heat by delivering more blood to the skin, increasing sweat rate while retaining electrolytes, and increasing plasma volume (the liquid component of blood, which allows more blood to be pumped to the skin for cooling). These physiological changes help to prevent hyperthermia and improve running performance in the heat.
In most of the country, the heat of summer is quickly giving way to the cold of winter. This means fewer sweltering, sweaty runs and more hats, gloves, and jackets to keep warm. It also means that runners will start to lose their heat acclimation.
Recently, exercise scientists have started studying whether heat acclimation can improve exercise performance in colder weather. Why is this? Well, expanded plasma volume is one of the main ways the human body responds to training, regardless of temperature. The idea is that training in the heat will cause the largest increase in plasma volume and cause a bigger improvement in running performance than training in cool to cold weather.
A preeminent researcher in this area is Dr. Christopher Minson; he and his colleagues at the University of Oregon have been studying the effects of heat training on cool weather exercise performance in endurance athletes (mostly cyclists). They’ve found heat training improves cool-weather VO2max, lactate threshold, and time trial performance compared to the same training protocol done in cool temperatures. Other researchers have tested the benefits of exercising in cool weather but then keeping core temperature high by immediately sitting in a hot tub or sauna after exercise. This post-exercise heat stress has been shown to elicit similar improvements in running performance compared to exercising in the heat. All these results suggest that heat training would improve running performance in cold-weather races.
Many runners will train through the winter in preparation for a spring marathon. Race-day temperature can vary greatly from year to year and an unseasonably hot day could derail months of dedicated training. You need look no further than the 2017 Boston Marathon, which was run on a very warm, sunny day. Most runners who trained through the winter were not heat acclimated and their finishing times suffered as a result. Heat training can help prepare runners to be able to handle a warm weather race that may otherwise derail a training cycle.
There is still a lot scientists must figure out. For example, might improvements simply be due to the increased stress of exercising in the heat, where the heart must work harder to supply enough blood to the muscles for exercise and the skin for cooling (suggesting the same benefits could be attained by simply training harder)? How long the benefits of heat training persist? What is the optimal exercise protocol (for example, heat training combined with high-intensity interval training has not been studied yet)? While not every study has shown a benefit of heat training, no study has shown that it impairs performance. This makes heat training a low-risk, high-reward investment in your training.
Interested in heat training but don’t have the high-precision heat chambers or ability to constantly monitor internal temperature (rectal probe) like the sports scientists do? Here is how you can make it work for you:
· Most of the benefits can be obtained with 7-10 consecutive days of exercise in the heat.
· You should exercise for an hour a day in a hot room. The temperature the room needs to be depends on a lot of things (humidity, airflow, exercise intensity). The simplest rule to follow: it should be hot enough that you sweat heavily.
· You can also try sitting in a hot tub or sauna 30 minutes after each run.
· Heat training should be stopped about 3 days before your goal race. This will give you enough time to recover, but you should retain most of the benefits.
· Hotter is not better and dehydration doesn’t help. Be sure to drink plenty of fluids and stop exercising if you begin to feel any symptoms of heat illness (read about that in detail here).
Hopefully after reading this you are warmed up to the idea (pun intended) that heat training can improve your race performance, regardless of temperature.
Daniel H. Craighead PhD
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