When exercising, your body can produce 10 times more heat than when resting. The evaporation of sweat is the primary way that this heat is dispelled and the body temperature is kept under control. So, if you are an average-sized individual, you might lose 2 quarts of sweat each hour of tennis play through evaporation, and even more in hot weather. This can hurt performance. Sweat loss reduces plasma volume (fluid part of blood) and subsequently the nutrient and oxygen supply to the working muscles. More important, the depletion of body water makes you more susceptible to heat-related illnesses.
The moisture in the air has a significant impact on your body's heat regulation process. High humidity, above about 80%, limits the evaporation of sweat because the air is already highly saturated with water. As a result, the cooling potential of vaporizing sweat is reduced or lost as the moisture simply pours off your body onto the court.
The combination of heat and humidity is reported as the heat index or the apparent temperature readings. This index gives you an idea of what the hot and humid air feels like to the average person. If, for instance, the air temperature is 85 degrees and the humidity is 85%, the apparent temperature is about 100 degrees. When heat index reports are 95 to 105 degrees, you will fatigue more quickly while exercising, and you are more susceptible to heat cramps and heat exhaustion. Above 105 degrees, there is a risk of heat stroke with prolonged activity.
By exercising regularly in hot weather, you can condition your body to the heat to some extent. Your body adjusts, for example, by increasing the liquid part of your blood. This improves sweating capacity and allows your body to store more heat with a smaller temperature gain. Heat acclimatization takes about seven to 14 days. However, it is lost in just a few days.
Water and salt are the main ingredients of sweat, and they don't smell. But sweat becomes unpleasant when associated with the growth and decomposition of bacteria. This happens when perspiration remains on the skin for a few hours and when the feet are encased in warm, airless shoes for a long time. In addition, the sweat from glands located in the armpits and groin often produces an odor since this moisture contains proteins and fatty materials that encourage bacterial growth.
Aging doesn't appear to seriously affect sweating, or how well we tolerate heat. It's true that during heat waves, older people are more susceptible to heat illness. But separating the effects of disease in such instances is often difficult. Moreover, many of these victims are unacclimated, unfit, and relatively obese.
Women in general have a lower sweat rate and higher percentage of body fat (which reduces heat loss) than men. This tends to make women a little less tolerant of the heat. However, for well-conditioned and relatively trim females, who are acclimatized to the heat, gender differences are negligible.
On a normal non-exercise day, you need to consume (in total) about 2 quarts of liquid to replace normal body fluid losses. Eight cups of this should come from drinking water and other beverages (except alcohol and caffeine drinks which increase urine production). The remainder, roughly two cups, comes from solid foods. Everything we eat contains water. Fruits and vegetables are 85% to 96% water, for instance, and even a steak is 50% water.
Water requirements increase dramatically. Approximately 1/2 to one quart of fluids per hour (2-4 cups) is required to replace the sweat loss during moderate physical activity. In hot weather, the liquid requirement during exercise is higher, depending upon temperature and level of play. In addition, you should drink several cups of water before play and again after the exercise is finished.