Overheating occurs when your body’s natural cooling system can no longer regulate your body temperature. Your body’s temperature rises during exercise. Combine this with hot, humid conditions, and you have a recipe for overheating. Heat exhaustion, characterized by weakness, muscle cramps, extreme thirst, dizziness, nausea, headache and pale skin, should be addressed immediately. Gone untreated, heat exhaustion can lead to the life-threatening condition heat stroke.
Body Temperature
Normal body temperature varies between 97.7 and 99.5 degrees Fahrenheit. When you exercise, your body produces heat due to the increases in muscle contraction. Core temperature can rise as high as 104 degrees Fahrenheit. If you exercise in hot conditions, exercise and the environment both cause a rise in your body temperature – potentially leading to overheating.
Sweating
The hypothalamus, located in the brain, works as your body’s thermostat by sending messages to different systems in the body to regulate temperature. When your body temperature rises due to hot weather, the body is signaled to increase the sweat rate to cool off. If the humidity is high, sweat doesn’t evaporate efficiently, causing a further increase in body temperature and potential overheating.
Dehydration
A hot environment can cause you to sweat more than normal, so you lose more fluids. When you are low on fluids, your body cannot perform optimally. When you are dehydrated by just 2 percent, your performance begins to decline, notes a review in the “Canadian Journal of Applied Physiology” published in 1999. One hour of exercise can result in a loss of more than a quart of water. If you do not replace these fluids, your body cannot cool itself through perspiration – resulting in dehydration and overheating.
Acclimatization
If you regularly train in the heat, your body responds by increasing the amount of sweat you produce during exercise and by turning on the signals to start sweating sooner. "Triathlon Magazine Canada" notes that your blood plasma volume will also increase, supporting your higher sweat rate and reducing stress on the heart – so you can go longer and harder in the heat. If you are not accustomed to training in the heat, you are more likely to become overheated when exerting yourself. If you are not acclimatized, you will lose twice as many electrolytes, which regulate muscle contraction, and fatigue sooner; your body will not be able to maintain an adequate rate of perspiration.