﻿﻿﻿﻿﻿﻿﻿﻿﻿Water: An essential part of any exercise, sport

﻿By David Pearce, M.D.

﻿Water is the most essential ingredient to a healthy life. Water has many important functions in the body including transporting nutrients and eliminating wastes, lubricating joints and tissues, temperature regulation through sweating and facilitating digestion.

Importance of water during exercise

Athletes need to stay hydrated for optimal performance. Studies have found that a loss of two or more percent of one's body weight due to sweating is linked to a drop in blood volume. When this occurs, the heart works harder to move blood through the bloodstream. This also can cause muscle cramps, dizziness and fatigue and even heat illnesses including heat exhaustion and heat stroke.

Causes of Dehydration
  • Inadequate fluid intake
  • Excessive sweating
  • Exercising in dry, hot weather
  • Drinking only when thirsty
  • Failure to replace fluid losses during and after exercise
Adequate fluid intake for athletes
Because sweat rates, losses and hydration levels of individuals vary widely, it is nearly impossible to provide specific recommendations or guidelines about the type or amount of fluids athletes should consume. Finding the right amount of fluid to drink depends upon a variety of factors, including the length and intensity of exercise and other individual differences. Here are two simple methods to estimate adequate hydration:
  • Monitoring urine volume output and color: A large amount of light colored, diluted urine probably means you are hydrated; dark colored, concentrated urine probably means you are dehydrated.
  • Weighing yourself before and after exercise: Any weight lost is likely from fluid, so drink enough to replenish those losses. Any weight gain could mean you are drinking more than you need.
Factors that affect fluid loss in athletes
  • Temperature: Exercising in the heat increases your fluid losses through sweating. Exercise in the cold can impair your ability to recognize fluid losses and increase fluid loss through respiration. In both cases, it is important to hydrate.
  • High altitude: Exercising at high altitudes increases your fluid losses and increases fluid needs.
  • Exercise duration and intensity: Exercising for hours (endurance sports) means you need to drink more frequently to avoid dehydration.
To find the correct balance of fluids for exercise, athletes should develop customized fluid replacement programs that prevent excessive dehydration (greater than 2 percent body weight loss from baseline body weight). The routine measurement of pre- and post-exercise body weights is useful for determining sweat rates and customized fluid replacement programs.

The Institute of Medicine says the need for carbohydrate and electrolyte replacement during exercise depends on exercise intensity and duration, weather and individual differences in sweat rates.

Carbohydrates provide energy for exercise over 60-90 minutes. This can also be provided through energy gels, bars and other foods.

Sports drinks can be helpful to athletes who are exercising at a high intensity for 60 minutes or more. Fluids supplying 60 to 100 calories per 8 ounces help to supply the needed calories required for continuous performance. It’s not necessary to replace losses of sodium, potassium and other electrolytes during exercise since you're unlikely to deplete your body's stores of these minerals during normal training.

If, however, you find yourself exercising in extreme conditions over 3 or 5 hours (a marathon or Ironman, for example) you may likely want to add a complex sports drink with electrolytes.

General guidelines for fluid needs during exercise
  • Drink 15-20 fluid ounces, 2-3 hours before exercise
  • Drink 8-10 ounces 10-15 minutes before exercise
  • Drink 8-10 ounces every 10-15 minutes during exercise
  • If exercising longer than 90 minutes, drink 8-10 fluid ounces of a sports drink (with no more than 8 percent carbohydrates) every 15-30 minutes.
  • Weigh yourself before and after exercise and replace fluid losses. After exercise, drink 20-24 fluid ounces of water for every one pound lost.
  • Consume a 4:1 ratio of carbohydrate to protein within two hours after exercise to replenish glycogen stores.