1. Fluid Retention/Regulation Pages 275-279

2. Water Loss in Heat:Dehydration Dehydration is an imbalance in fluid dynamics when fluid intake does not replenish water loss –No matter what type of exercise there is always water lost –Even non-exercise induced water loss also occurs, such as when “power” athletes attempt to “make weight” through rapid weight loss induced by common dehydration techniques, such as a sauna or steam room. –The risk of heat illness increases when a person begins exercising in a dehydrated state.

3. Magnitude of Fluid Loss In an acclimatized person, water loss by sweating averages nearly 12 liters (26 lbs) on a daily basis Several hours of exercise can cause the sweat glands to become fatigued, which can in turn, impair core temperature. Marathon runners lose about 5 liters of fluid during competition, which accounts for 6-10 % of body mass Wrestlers usually compete in a dehydrated state in order to make their weight

4. Consequences of Fluid Loss Just about any degree of dehydration impairs physiologic function and thermoregulation. As dehydration progresses and plasma volume decreases, peripheal blood flow and sweating rate diminish and thermoregulation becomes difficult Increased Heart rate Decreased blood flow to the skin Reduction in circulatory and temperature- regulating capacity to meet metabolic and thermal demands of exercise.

5. Fluid Loss in Winter Colder air contains less moisture, thus there is a greater fluid volume leaving the respiratory passages as incoming air becomes humidified and warmed to body temp. Causes up to 1 liter of fluid loss Cold stress stimulates an increase in urine production. Some people overdress

6. Diuretic Use Plasma provides a greater percentage of water loss from diuretic-induced dehydration Diuretic drugs can also impair neuromuscular function Vomiting and diarrhea are not good ways to “make weight” because they produce dehydration and cause excessive mineral loss.

7. Rehydration Adequate fluid replacement sustains the exceptional potential fro evaporative cooling of acclimatized humans Athletes/people should properly schedule fluid replacement to maintain plasma volume so that circulation and sweating progress at optimal levels Drinking water can increase blood flow to the skin for more effective cooling –This prevents dehydration and its associated consequences

8. Rehydration For wrestlers, dehydration is a way of life so they can compete at a lower weight. This is also seen in ballet dancers A well-hydrated athlete always functions at a higher physiologic and performance level than a dehydrated one

9. Pre-Exercise Hydration Drinking extra water before exercising in a hot environment provides some protection against heat stress because it delays dehydration, increases sweating during exercise, and minimizes use in core temp. Recommended consumption is between 400 and 600 mL (13-20 oz) of cool water 20 minutes before exercise in heat. –This increases stomach volume, but does not replace fluid uptake during exercise

10. Adequacy of Rehydration Changes in body weight indicate the extent of water loss during exercise and the adequacy of rehydration during and after exercise or athletic competition. Dark yellow urine with strong odor indicates inadequate hydration. Each lb of weight loss after exercise represents 450 mL (15 fl oz). Water must be available during practice and competition.

11. Sodium Facilitates Rehydration A small amount of sodium added to a rehydration beverage facilitates more complete rehydration than plain water Restoring water and electrolyte balance in recovery occurs by: –Adding moderate to high amounts of sodium to the drink –Combining solid food with plain water

12. Sodium Facilitates Rehydration Because the kidneys continually form urine, the volume of ingested fluid following exercise must be larger (usually by 25-50%) than exercise sweat loss to restore balance. If too much sodium, the excess fluid intake merely increases urine output with no benefit to rehydration. With prolonged exercise in heat, sweat loss can deplete the body of 13-17 g of salt per day. A glass of OJ or tomato juice replaces almost all the potassium, calcium, and magnesium excreted in about 3 liters of sweat.