Heat Acclimatization
If You Can’t Stand The Heat….
Ah Summertime! School’s out, the days are longer, the outdoor nationals are in full swing and Loretta’s is right around the corner! Just like at the outdoor nationals, you are probably experiencing the crushing onset of real heat with only worsening conditions to look forward to as summer draws to a close. Your body is equipped with mechanisms that allow you to adapt to these harsh conditions in a process called heat acclimatization. The most important of these mechanisms revolve around the process of sweating which helps keep your core temperature in check through evaporative cooling. Proper acclimatization causes the following sweat related physiological changes:
lower core temperature required to start sweat response (start sweating earlier)
higher volume of sweat (more potential for greater evaporative heat loss)
increased plasma volume (decreases heart rate and allows for more sweat loss before large decrements in performance. Temporary but is replaced by other changes that have the same end effect)
decreased skin temperature (helps keep core cooler and decreases perceived exertion)
conservation of sodium chloride (helps maintain proper electrolyte and ionic balance)
Complete heat acclimatization takes up to two weeks but the more fit you are the less time it takes. There is no magic formula; a decrease in exercise intensity and duration with the onset of heat that is gradually increased over the course of the acclimatization period is a general guideline. You must also increase fluid intake during this time and it has also been shown that increasing electrolyte intake during this period aids in acclimatizing. It is important to remember that trying to maintain the same level of exercise intensity if you are not acclimatized is a sure fire way to start overtraining. Willpower cannot overcome the rules of physiology so always respect what your body is telling you when acclimatizing to the heat.
Becoming acclimatized to the heat actually increases your fluid intake requirements since your sweat volume increases and your plasma volume is higher. This means you have to increase fluid intake both during exercise and throughout the day. A good way to estimate how much fluid you require during training is to weigh yourself before (naked and dry) and then again after the first 100 minutes of training to measure your weight loss. One pound of weight loss means drinking half a quart of fluid as replacement. If you track what you did drink and add what you are required to drink to maintain your body weight, you can formulate a drinking rate that will keep you as close as possible to a zero net loss of fluid weight. Relying solely on your thirst mechanism to drink will always leave you behind in the fluid balance race. Drink on a schedule and before you are thirsty to ensure adequate hydration. Using drinks with electrolytes (found in most sports drinks) can help with both acclimatization and performance in the heat due to the body’s quest to retain sodium chloride and plasma volume.
Another important consideration is that heat acclimatization is specific to humidity. The adaptations are different for hot/dry environments vs. hot/humid environments so it is best to plan your acclimatization strategy to match your specific race environment.
Heat acclimatization reverses itself rather quickly once the heat stress is removed. Heat acclimatization will be retained for one week but 75% of the adaptations are lost within three weeks. More frequent exposures to heat/more exercise sessions in heat will slow this rate of loss. Similarly, leaving the hot environment during the acclimatization process will extend the total period of time it takes to become fully acclimatized. The most efficient acclimatization process takes place when you can stay in the hot environment for the entire time period required to acclimatize.
Motocross is a very physically demanding sport. Heat only adds to the demands placed on your hard working body. Proper heat acclimatization will help you perform to your potential and help you avoid heat related injuries ranging from heat cramps all the way to heat stroke. Make sure all your hard work and dedication are not hampered due to the hot environment at the races – acclimatize properly and make sure you can handle the heat!