Hydration (from
http://www.timinvermont.com/fitness/faq18.htm#Hydration )
An inactive person requires a minimum of 1.2 liters (40 oz) of water a day to keep all body systems functioning properly. Some level of activity (walking around, normal daily actions) doubles this requirement. High humidity again can double the needed amount, as can hard exercise. It may not be unusual to reach a need of 8-10 liters (2 - 2.5 gal) a day.
To adequately rehydrate yourself at the end of the day, drink water slowly, one glass at a time, until you have to "answer the call". Then continue to drink more water, until the need arises a second time.
Remember that caffeine and alcohol are diuretic, so consuming coffee, tea, beer, etc, will cause the body a net LOSS of water. One indicator of insufficient water intake is the color of urine - the darker it is, the more water you need. (However other medical conditions and drugs may also have a discoloring effect.) Since your body runs on autopilot for six to eight hours while you are asleep, try to get enough water in the evening. This may allieviate the snacking urge a little, and your kidneys will be much happier, too.
Exercising in hot weather means dehydration, no question about it. The body cools itself by circulating blood closer to the skin, and through sweating. Dehydration makes these cooling mechanisms less efficient, leading to more rapid fatigue and a higher risk of heat exhaustion and heatstroke. In tests, cyclists who did not have adequate water intake experienced significantly faster heart rates at lower speeds than the control subjects, who were well hydrated.
Symptoms of dehydration after a workout include heavy fatigue, lethargy, headache, dizziness and nausea. These may persist for a day or longer without adequate water replacement. Dehydration is common. Normal sweating during exercise in heat means between a 2 to 6% loss of bodyweight. (As an example, a 180 lb man could lose 7 pounds of water.) Also, acclimation to heat means a person gets more efficient at cooling off - through sweating and blood circulation - so an acclimated person requires MORE water, rather than less.
How much water should you drink in hot weather?
- 500ml (16 oz) 2 hrs before exercise
- 250-500 ml (8-16 oz) right before exercise
- Weigh yourself before and after exercise and drink 500 ml (16 oz) for
each 0.5 kg (pound) you lose.
Cool water 4.4 - 10 C (40-50 degrees F) is easiest for the body to absorb - better than very cold water. A 5-7% sugar solution (no higher!) may speed absorption and assist recovery.
It is possible to drink too much water. The effects can include nausea, convulsions, and vomiting. The condition is called hyponatremia, an excessively low sodium concentration in the blood due to dilution. On the same lines, "water intoxication" has occurred in marathoners and others engaging in prolonged activity. Apparently one physiological adaption to exercise is the release of antidiuretic hormones and a slowing of kidney functions.
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