Hydration and Effects of Dehydration
Fluid guidelines for before, during, and after exercise have been prepared to help athletes and active individuals to properly hydrate themselves.
- Before exercise 12-20oz of fluid 2 hours before exercise
- During exercise 5-8.5oz of water or sports drink every 15-20 minutes of exercise
- After exercise 16oz of water or sports drink for every pound of body mass lost during exercise
You should pre-hydrate several hours before exercise to allow for fluid absorption and urine output. The goal of drinking during exercise is to keep fluid losses to 2% or less; because as dehydration levels in excess of this can lead to significant performance decrements. Fluids should be cool, not cold, to promote consumption and optimize gastric emptying. Rehydration practices should aim to fully replace fluid and electrolyte losses. Those beverages containing sodium will help the body stimulate thirst and retain ingested fluids. For those individuals needing to achieve rapid and complete recovery from dehydration, approximately 1.5 L of fluid should be consumed for every 2.2 pounds of body mass lost after exercise. The Institute of Medicine (IOM) has recommended that replacement beverages contain sodium, potassium, and carbohydrates for prolonged activity in hot weather.
Eating food also promotes fluid intake and retention; therefore, adequate meals and snacks throughout the day are critical to daily hydration practices. Evidence suggests that caffeine consumed in foods and beverages at levels less than 180 mg .d -1 will likely not increase urine outputs or cause dehydration. Food and beverage manufacturers are not required to list caffeine amounts; however, as a reference, an average cup of home-brewed coffee contains approximately 100 mg caffeine and a 250ml commercial, gourmet black coffee can range between 200-350 mg. On the other hand, alcohol can delay full rehydration because it can act as a diuretic and increase urine output. Therefore, alcohol consumption should be limited, especially in the several days prior to competition or intense training and the post-exercise period.
You can monitor your own hydration status through a number of ways. Body mass changes, urine color, and thirst can all indicate the need for additional fluids. Measuring body mass before and after exercise and calculating the difference will give an athlete an indication of his or her sweat rate. Having an idea of what one’s sweat rate is can help determine fluid that needs to be replaced after exercise. Monitoring urine color that is pale yellow or like light-coloured lemonade is desirable and likely indicates a well-hydrated state for the runner. Darker colors, like apple juice, would indicate that the athlete should drink additional fluids. In addition to these self-monitoring techniques, precise readings of urine-specific gravity can be measured with a refractometer and can be used as another general indicator of hydration status. Well-hydrated states are reflected by readings of less than 1.01, whereas readings of more than 1.02 indicate dehydration.
Also, the smell of ammonia in sweat is common among athletes . Ammonia comes from the breakdown of proteins in the body for fuel (glucose) which produces nitrogen as a by-product. Nitrogen is then processed by the kidneys which become overloaded, and instead of the N being excreted as urine it ends up as ammonia in sweat. To remedy this common running condition, consume adequate fluids and the ammonia will be diluted!
Dehydration refers to the water loss in the intracellular and extracellular compartments, and this can rapidly reach levels that reduce the body’s ability to dissipate heat. It can increase the rate of heat storage and cardiovascular strain due to a reduction in sweat rate and skin blood flow. 70% of the human body is composed of water and fluid loss can cause impaired athletic performance, which becomes apparent at 1-2% of the body weight has been lost as sweat. This may be attributed to a reduction in blood plasma volume, reduced skin blood flow and a general deterioration in circulatory/thermoregulatory efficiency.
Dehydration associated with 3% decrease in body weight also slows gastric emptying, thus increasing stomach cramps and fatigue. When fluid loss amounts to 4-5% of the body weight the running capacity is reduced by 50% due an elevated heart rate and a reduced stroke volume. Further fluid losses are likely to lead to collapse, and this does occasionally happens during long distance running events in warm weather conditions. However, marathon runners frequently experience a 6-8% loss of body weight and this has been attributed to an exceptional potential for evaporative cooling ; with adequate fluid replacement.
Dehydration Signs and Symptoms
Active individuals should be familiar with dehydration warning signs and be able to recognize these symptoms before heat illness progresses. Early signs and symptoms include thirst, discomfort and complaints. These are generally followed by flushed skin, muscle cramps, and apathy. As water loss continues, dizziness, headache, vomiting, nausea, chills, and shortness of breath may be observed. Identifying these signs and symptoms can help prevent exertion heat illness and potentially life-threatening conditions.