Fluid Retention/Regulation

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.