Staying hydrated is essential for everyone, but athletes
have an even greater need to drink and replace fluids during exercise. Water is
the most important nutrient for life and has many important functions including
regulating temperature, lubricating joints and transporting nutrients and waste
throughout the body.
Hydration During Exercise
Staying hydrated is particularly important during exercise.
Adequate fluid intake is essential to comfort, performance and safety. The
longer and more intensely you exercise, the more important it is to drink the
right kind of fluids.
Dehydration
Decreases Performance
Studies have found that athletes who lose as little as two
percent of their body weight through sweating has a drop in blood volume which
causes the heart to work harder to circulate blood. A drop in blood volume may
also lead to muscle
cramps, dizziness, fatigue and heat
illness including:
- Heat Exhaustion
- Heat Stroke
- Inadequate fluid intake
- Excessive sweating
- Failure to replace fluid losses during and after exercise
- Exercising in dry, hot weather
- Drinking only when thirsty
What Should Athletes Drink
Because there is wide variability in sweat rates, losses and
hydration levels of individuals, 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 individual factors including the length and intensity of exercise
and other individual differences. There are, however, two simple methods of
estimating 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 try to drink enough to replenish those losses. Any weight gaincould mean you are drinking more than you need.
How Athletes Lose Water
- High altitude. Exercising at altitude increases your fluid losses and therefore increases you fluid needs.
- Temperature. Exercising in the heat increases you fluid losses through sweating and exercise in the cold can impair you ability to recognize fluid losses and increase fluid lost through respiration. In both cases it is important to hydrate.
- Sweating. Some athletes sweat more than others. If you sweat a lot you are at greater risk for dehydration. Again, weigh yourself before and after exercise to judge sweat loss.
- Exercise Duration and Intensity. Exercising for hours (endurance sports) means you need to drink more and more frequently to avoid dehydration.
To find the correct balance of fluids for exercise, the American
College Of Sports Medicine suggests that "individuals should
develop customized fluid replacement programs that prevent excessive (greater
than 2 percent body weight reductions from baseline body weight) dehydration.
The routine measurement of pre- and post-exercise body weights is useful for
determining sweat rates and customized fluid replacement programs. Consumption
of beverages containing electrolytes and
carbohydrates can help sustain fluid-electrolyte balance and exercise
performance."
According to the Institute of Medicine the need for
carbohydrate and electrolytes replacement during exercise depends on exercise intensity,
duration, weather and individual differences in sweat rates. [They write,
"fluid replacement beverages might contain ~20–30 meqILj1 sodium (chloride
as the anion), ~2–5 meqILj1 potassium and ~5–10% carbohydrate."] Sodium
and potassium are to help replace sweat electrolyte losses, and sodium also
helps to stimulate thirst. Carbohydrate provides energy for exercise over 60-90
minutes. This can also be provided through energy gels, bars, and other foods.
What about Sports Drinks
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 helps to supply the needed calories required for continuous
performance. It's really 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,
Ironman or ultramarathon, for example) you may likely want to add a complex
sports drink with electrolytes.
General Guidelines for Fluid Needs During Exercise
While specific fluid recommendations aren't possible due to
individual variability, most athletes can use the following guidelines as a
starting point, and modify their fluid needs accordingly.
Hydration Before Exercise
- Drink about 15-20 fl oz, 2-3 hours before exercise
- Drink 8-10 fl oz 10-15 min before exercise
Hydration During Exercise
- Drink 8-10 fl oz every 10-15 min during exercise
- If exercising longer than 90 minutes, drink 8-10 fl oz of a sports drink (with no more than 8 percent carbohydrate) every 15 - 30 minutes.
Hydration
After Exercise
- Weigh yourself before and after exercise and replace fluid losses.
- Drink 20-24 fl oz water for every 1 lb lost.
- Consume a 4:1 ratio of carbohydrate to protein within the 2 hours after exercise to replenish glycogen stores.
Hyponatremia
- Drinking Too Much Water
Although rare, athletes can drink too much water and suffer
from hyponatremia (water
intoxication). Drinking excessive amounts of water can cause a low
concentration of sodium in the blood - a serious medical emergency.