STAY COOL IN HOT WEATHER
BY STAFF WRITER
The South African Summer is here! Early sunrises and training sessions are usually supported by moderate temperatures in SA, but the midday and late afternoon temperatures may often exceed 30°C. The central areas of South Africa have been known to achieve temps in the low 40s! Even a small and unusual increase in the temperature will require the body to adapt.
So, at what temperature does the body begin to exhibit a heat response? If the apparent temperature is above 16°C with a 60% humidity, then dehydration, hyponatremia, heat exhaustion and cramps are more likely to occur. It is important to remember the response will differ depending on the athlete and the length and intensity of exercise. The ability to physiologically acclimatize to hot or extremely hot conditions requires 14-21 days. This is achieved when the salt concentration of sweat progressively decreases while the volume of sweat increases. Urine volume also reduces. In addition, vasodilation of peripheral blood vessels results in increased heat loss through radiation. Vasodilation also causes flushing, or reddening, of the skin since more blood is close to the surface.
The body’s ability for adaptability in extremely hot climates or due to an internal infection, may cause the core body temperature to rise to dangerous levels. Hyperthermia, a life-threatening disorder, typically starts in humans when body temperatures rise to 40.6-41.7° C. While exercising, athletes will lose heat to the surrounding environment by 4 pathways:
- Radiation of Heat Waves - 60%
- Evaporation of Sweat - 22%
- Convection of Air Currents - 15%
- Conduction to Objects - 3%
There are limits to how much heat the body can withstand during exercise. But there are ways by which adaptation to heat stress may be improved. Simple radiation is responsible for most of the loss during normal temperature range, but in hot dry climates evaporative cooling and sweating is more significant. Adapting to hot environments is complex. The effect of heat on human bodies varies with the relative humidity of the air. HIGH TEMPERATURES + HIGH HUMIDITY makes it very difficult to lose excess body heat. This is due to the fact that when the moisture content of air goes up, it becomes increasingly more difficult for sweat to evaporate. As a result, we do not get the cooling effect of rapid evaporation. In DRY HOT weather, humidity is low and sweat evaporates readily. The higher the temperatures, the more significant of a cooling effect we get from evaporation.
Similarly, the human body has a variety of ways to absorb fluids, electrolytes and calories. This all points to different strategies (and products) to achieve your ideal fluid and electrolyte intake. Fluids are absorbed in the stomach first and then a few minutes later in the small intestines. Carbohydrates rely on sodium molecules to cross gut linings, so some sodium is absorbed with carbohydrates. HEED supplies high glycemic carbohydrates with a moderate level of electrolytes to aid this process. The electrolytes sodium, chloride and potassium are absorbed at a high rate by the colon so it will sometimes be necessary to consume an electrolyte only source such as Endurolytes Extreme. Fluid loss and body core temperature elevation drive thirst to increase fluids and this is good to a point. But loading too much water volume without electrolytes may create a low serum sodium level or hyponatremia, an event-ending medical emergency. Hence the reason for a quality electrolyte or hydration product such as FIZZ.
Tips for training in the heat:
- Distance Training at Aerobic Pace 14- 21 consecutive days
- Train the body to refuel, rehydrate, and process electrolytes during exercise.
- Train at a reduced pace to compensate for overheating
- Dilute rehydration solutions, slightly increase electrolytes
- Increase fluid volume cautiously; resist drinking above 830ml per hour
- Keep head, trunk, & quads WET to increase evaporative heat loss
The human body will adapt within 21 days with aerobic heat stress exposure. (DO NOT wear extra clothing or plastic sweat suits to raise body core temperatures in preparation for a hyperthermic event). If body core temperatures exceed evaporative cooling rate, fluid loss and electrolyte loss will present as dehydration, tachycardia, excessive heart rate, dizziness, gastric shutdown, performance deterioration, muscle cramping, and the athlete will be forced to reduce pace or stop exercising. When body core temperatures exceed the evaporative cooling rate, drinking cold fluids and emersion in cold water are the fastest remedies to reduce body core temperatures. Keep in mind, maintaining a slower pace (lower gears, easy cadence) in the heat may mean a better finish place over the course of a hyperthermic endurance event. It is best to be able to complete adaptive training in the heat with race event light coloured clothing, exposing as much skin as possible.
Ultimately, your preparation and understanding of how you body adapts to heat will help you adjust your race strategy and achieve your best result.