Heat Training: Does it Boost Running Performance?
For endurance athletes, finding ways to boost performance without taking performance enhancing drugs is always of utmost concern. Long distance runners and cyclists take multiple naps per day to increase natural levels of human growth hormone; nutrition and hydration is dialed in to improve performance and recovery; and some athletes even count the number of steps they take each day to minimize time spent on one’s feet. Now, exercise scientists are saying there is a new way to elicit performance gains: by enduring heat training.
This is not about how to survive heat, it’s about how to embrace high temperatures and use this as an advantage. Below is part of the research I found on heat training and its similarities to altitude training when it comes to running performance. As I mentioned, this article is not about how heat affects your training in a bad way, it’s about how you should use it while training for a race in order to make those muscles suffer less and prolong the time before anaerobic modes kick in.
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High performance training contains two basic principles: stress and recovery. The goal of physical exertion is to teach the body to adapt to stress, thereby making the aerobic, skeletal and muscular systems stronger in the process. In between workouts, the “little things” such as rest, nutrition, hydration and muscle repair are controlled as much as possible in order to help the body best adapt to the stresses of the training. Stress adaptation is one reason why athletes train at altitude. Being in an oxygen deprived environment, even for as short as one week, causes many immediate benefits: natural levels of EPO increase, resulting in increased red blood cell production and, more importantly, running becomes significantly harder at the same effort put forth at sea level. Therefore, runners receive an immediate mental and physical benefit from having to push through the pain and discomfort that even easy training runs provide.
Heat Training as the New Altitude Training?
Not all athletes are able to benefit from altitude training, and some research has even shown that altitude training may be detrimental for certain individuals. In fact, many scientists now believe in a “train high but live low” philosophy, whereby athletes train in the mountains, but return to sea level for the rest of their day in order to maximize recovery. Heat training, however, has been suggested to circumvent the main disadvantages of altitude training, while still providing the important stress adaptation benefits. There are numerous studies1 on this fact.
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Ask any endurance athlete the question of whether they would prefer training in 90-degree heat and high humidity or 50-degree temperatures and low humidity and the answer is sure to be the latter. Running for long distances in the heat not only feels physically harder, but times are significantly slower. This calculator displays just how much heat plays a role in running times. A 30:00 5k on a 60-degree day equates to a 31:21 5k on a 90-degree day. Therefore, when training in the heat athletes are able to reap the benefits of additional stress during training, but then immediately return to the air conditioning for optimal recovery.
Backed by Science
Sure, in theory heat training sounds like a great way to adapt to stress, but has this been backed by science? The answer is yes. Two important studies have been performed that link improved performance to heat training stints. The first was a study performed by the University of Oregon2 which tested the ability of cyclists to perform a time trial after spending time training in hot conditions. Twelve high performance cyclists spent 10 days training in a 100-degree room for 100 minutes per day and experienced an amazing 7% boost in performance in a subsequent time trial in cool conditions. The control group, who performed all of their training in 55-degree temperatures, did not receive a performance boost in the same trial.
A second study, performed at the University of New Zealand, tested the benefits of heat training on rowers3. In this experiment, rowers were subjected to five 90 minute training sessions in a room that was 104 degrees and 60% humidity. After the training stint, rowers saw a 1.5% improvement in their 2,000 m rowing times. These results have led to a greater awareness of the role that stress adaptation plays within the endurance athlete’s body.
Physiological Benefits of Heat Training
What exactly are the mechanisms of heat training and how does overheating the body lead to the impressive gains in performance that scientists have reported?
Perhaps the most beneficial adaptation that the body makes when training in the heat is increased plasma volume. Like the increase in red blood cell count that is experienced during altitude training, the increase of plasma volume (shown to be between 4 – 7% in the above mentioned studies) leads to improved VO2 max, which is a measure of the amount of usable oxygen in an athlete’s system. Blood plasma is also responsible for hydrating tissues and transporting electrolytes throughout the body. While red blood cell production is important, RBCs do not function while the body is dehydrated, whereas increased plasma volume will help the body perform even in a dehydrated state.
When training in the heat, dehydration is an important consideration. Some researchers actually believe that a moderate level of dehydration is important for gaining physiological benefits. By training, and adapting, to a dehydrated state, performance gains can be expected when the body performs with optimal hydration on race day. In addition, an important regulatory component is Heat Shock Protein 70 (HSP70) which protects the cells from heat stress. When training in hot, dehydrating conditions, the amount of HSP70 in the body increases, leading to improved ability to handle stress.
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A Practical Example
While the research on heat stress and running is scarce, there is one practical example of a runner who used intentional heat training to her advantage. In the 2016 Olympic Marathon Trials, which were held in Los Angeles in record setting heat, Alia Gray credited her great performance with elements of heat training during her marathon build up. Alia Gray finished 10th at the Trials with a huge PR despite having been diagnosed with a stress fracture just two months before the race. She speculates that by performing her cross training on an alter-G treadmill in a hot room her body was better able to adapt to the unprecedented heat that caused nearly 25% of the field to drop out, and only a handful of athletes (out of the nearly 500 who competed) to run a personal best time.
How to Heat Train
How should an athlete heat train in order to receive maximum benefit? Runners can take one of two approaches, either by heat training for 5–10 days straight before an important competition, or by incorporating 1–2 heat sessions per week over a period of 10–12 weeks. Athletes are cautioned to respect the heat and slow down in their workouts, as the point is to simply stress the body. After a few days of acclimation, moderately paced workouts can be incorporated. In addition, runners should try to limit water consumption (if safe to do so), aiming for 2-3% dehydration at the end of each training session.
1. Armstrong LE, Maresh CM., The induction and decay of heat acclimatisation in trained athletes, Sports Med. 1991 Nov;12(5):302-12 (link)
2. Lorenzo S, Halliwill JR, Sawka MN, Minson CT. Heat acclimation improves exercise performance. Journal of Applied Physiology. 2010;109(4):1140-1147. doi:10.1152/japplphysiol.00495.2010. (link)
3. Garrett AT, Creasy R, Rehrer NJ, Patterson MJ, Cotter JD, Effectiveness of short-term heat acclimation for highly trained athletes, Eur J Appl Physiol. 2012 May;112(5):1827-37. doi: 10.1007/s00421-011-2153-3. Epub 2011 Sep 14. (link)