Many people look forward to summer temperatures after several months of winter cold. People like to get outside and become more active as the temperature rises. As summer approaches, it becomes important to become acclimated and be adequately hydrated to avoid heat illness. This document will discuss physical adaptations to heat, hydration, and heat illness with treatment if necessary.

As most people are aware, normal body temperature is 98.6 degrees Fahrenheit or 37 degrees Celsius and is influenced by environmental conditions and physical activity. During exercise, there is a rise in body temperature from increased blood flow and heat produced by muscle contraction. In response, heart rate is elevated to accommodate muscle contraction, but also to dissipate heat through the skin. Sweating is also initiated. During physical activity of sufficient intensity, the body may produce heat up to fifteen to twenty times greater than at rest. Approximately twenty-five percent of energy expended is a result of activity, but the remaining seventy-five percent is released by the muscle as heat. The body dissipates this heat by conduction, convection, radiation, and evaporation as sweat. Hyperthermia is a rise in body temperature that can lead to injury if the body exceeds 102.2 degrees Fahrenheit or 39 degrees Celsius. Symptoms of heat stress in the body may include the following: higher than normal heart rate during exercise, very rapid breathing, pale skin, severe thirst or dehydration, confusion, dizziness, disorientation, heat cramps, or other illness.

During exercise in a hot environment, it is important to adapt to conditions and be hydrated correctly. There are factors that affect the ability to perform in various conditions. These factors include intensity and duration of activity, aerobic capacity or VO2 maximum, acclimatization to selected conditions, exact environmental conditions, hydration level, and personal issues such as sleep, supplements, and medications. All these factors influence the ability of an individual to respond to environmental stressors whether in the form of increased heat or cold exposure.

Heat is dissipated by the natural process of perspiration or sweating. In a hot environment during prolonged exercise, blood flow to the skin and sweat may start to decline with fluid deficits of three to five percent. Water loss of greater than two to three percent of bodyweight can lead to a decrease in performance. For this reason, proper hydration is recommended before, during, and after exercise. Everyone who is active wants to be properly hydrated when engaging in an exercise session. The consumption of water or sports drinks at five to seven milliliters per kilogram of bodyweight or two to three milliliters per pound at least four hours before exercise is recommended for proper hydration. A two hundred twenty-pound man weighs one hundred kilograms. The recommendation calls for five to seven milliliters per kilograms of bodyweight. In this case, we multiply one hundred kilograms by seven to yield seven hundred milliliters. One milliliter is equal to .034 of an ounce. So, 700 x .034 = 23.8 ounces. This person should consume twenty-four ounces of water or sports drinks at least four hours before a scheduled exercise session. Additional fluid may be necessary if this level does not lead to urine production or urine is dark. In these circumstances, greater fluionsumption may be necessary for optimal exercise performance.

After exercise, the need to replenish fluid and electrolytes is of utmost importance for recod cvery from and adaptation to exercise. Consumption of adequate meals with the appropriate amount of sodium and water intake should restore normal hydration level. Large water consumption in a short time frame will cause urine production and may not be optimal for rehydration. In the case that a short recovery time is necessary, a rapid recovery schedule may use one and a half liters per kilogram of bodyweight loss can be used to account for increased urine production.

The goal during an exercise session is to prevent excessive dehydration and changes in electrolytes. To prevent these conditions, bodyweight should be considered with a two percent or more loss may indicate excessive dehydration when compared to the pre-exercise values. Fluid intake of .4 to.8 liters per hour for marathon runners is recommended. Higher rates may be necessary for faster or heavier runners in warmer environments and lower rates for slower or lighter runners in cooler environments. Because of genetics and individual as well as environmental variability, the importance of pre- and post-exercise bodyweight monitoring cannot be overstated. When an exercise session is over forty-five minutes or more in duration or involves higher intensity intermittent training, a carbohydrate or electrolyte solution or beverage may be more beneficial than water alone. These beverages should provide six to eight percent of carbohydrate in solution. Many sports drinks that present this percentage of carbohydrates and electrolytes are beneficial to replace losses due to sweat. It is important to understand at concentrations greater than eight percent will hinder absorption and therefore is not recommended. Beverages at these higher concentrations will not provide the desired results and may be detrimental to performance. For these reasons, concentrations of greater than eight percent are not recommended for optimal performance. Proper hydration is very important in hot environments and as treatment of heat related illness. Other treatments for heat related problems or illness include to stop exercising, move to shaded or air-conditioned area, remove excess clothing or equipment, sit in front of a fan, put a cold cloth or compress on the back of the neck, or submerge the entire body in cold water when possible. If the symptoms are present or persist after such treatments, contact emergency personnel immediately. Severe heat illness can be fatal or cause permanent health problems if not sufficiently treated in a timely manner If you experience heat related symptoms, stop exercising and seek help immediately. It is always better to be safe now instead of sorry later. For more helpful articles concerning nutrition and training, visit our blog at