Unfortunately, though, there’s no one size fits all approach: different environmental factors will have different effects, depending on what type of exercise is called for. For instance, while endurance athletes are exposed to heat for long periods of time, they are working at a lower intensity and have more opportunities to drink and rehydrate, compared with, say, sprinters.
For this reason, coaches seeking to get the best performance out of their athletes are better off thinking of high body temperature (hyperthermia) and dehydration as the critical factors, rather than the weather alone.
Turning up the heat
There are three common causes of hyperthermia in athletes: high exercise intensity, high air temperature and high relative humidity. Any athlete – female or male – who pushes themselves too fast, for too long, in hot and humid conditions can experience performance-degrading hyperthermia.
Hyperthermia affects physical performance in a few key ways. It reduces muscular endurance, or the ability to sustain muscular contractions over time. This can worsen performance in long-distance events such as cycling, track and field and soccer. It doesn’t have much impact on sports such as weightlifting, however, because it doesn’t dramatically alter the maximum strength which muscles can exert.
Hyperthermia also changes the way that our bodies generate energy, from aerobic metabolism (which requires oxygen, and burns carbohydrates and fat) to anaerobic metabolism (which does not require oxygen, and mainly burns carbohydrates).
In practice, this means that in higher temperatures, the carbohydrates stored in the body will be consumed more quickly. In this way, hyperthermia will affect competitors such as endurance road cyclists and marathon runners, who depend heavily on carbohydrate stores in the body.
What’s more, hyperthermia causes the blood vessels in the skin to dilate, and blood to pool in the limbs. This reduces the volume of blood that returns to the heart, which in turn reduces the amount of oxygen-rich blood being pumped from the heart, and increases strain on the circulatory system. These effects are manifested as increased fatigue.
To fight the ill effects of hyperthermia, athletes often prepare by completing a process of heat acclimatisation. This usually involves a daily bout of exercise under heat stress – where the athletes’ core temperature is raised for one to two hours in an artificially heated environment – over five to 16 days.
Scientists have observed that acclimatisation exercises cause athletes to begin sweating sooner and at faster rates. It also makes blood vessels in the skin dilate earlier and reduces strain on the heart. This, in turn, reduces the body’s core temperature and improves endurance during exercise in the heat.
Research on this topic is constantly being advanced different teams tweak their acclimatisation protocols to make those marginal gains, which can mean the difference between winning and losing.
To perform at their peak in unfamiliar environments, athletes must also maintain the correct fluid levels before, during and after their events.
Over the past ten to 15 years, many scientific papers have extensively reviewed the effects of exercise-induced dehydration, and most agree that it significantly impairs performance. Dehydration occurs when athletes don’t drink enough before the competition, or can’t drink enough during it to replace the water lost through sweating.
Obviously, exercising in the heat will cause athletes to lose more fluid through sweat than exercising in cooler conditions. Consider this: exercise at a moderate intensity results in whole-body sweat losses of between 0.8 and 1.4 liters per hour. By comparison, the highest sweating rate ever reported for an athlete was 3.7 litres per hour, during the marathon of the 1984 Summer Olympic Games.
Author: Alberto Dolci, Course leader MSc Sport & Exercise Nutrition, Lecturer in Exercise & Environmental Physiology and Exercise Immunology, University of Westminster
Courtesy: The Conversation