If it's hot outside, and you're outside, stay hydrated

Whew, it's hot. Sweat leaking from pores, still two miles to go, and you need to what? That's right, drink water.

Fortunately, humans have a built-in water meter, an innate ability to detect the need for H2O. It's called thirst.

Even so, workouts in summer temperatures can deceive thirst. Once it sets in on a hot day, the body requires immediate relief.

Dehydration can trigger all sorts of awful things - dizziness, cramping, headaches, even death in extreme cases. At-risk groups are active people, like runners and cyclists, and those who work outdoors for extended periods - roofers, landscapers, construction workers.

Too much water also can be dangerous. The Beverage Institute for Health & Wellness says over-hydration typically affects only endurance athletes, specifically "slower runners in marathon events" who drink more than they sweat.

All that drinking can dilute blood sodium levels, which may cause seizures, confusion, disorientation and even the possibility of death. The trick is to be able to match sweat loss with just the right amount of fluid and electrolyte replacement.

USA Track and Field's new hydration guidelines recommend that athletes "be sensitive to the onset of thirst as the signal to drink, rather than staying ahead of thirst. Being guided by their thirst, runners prevent dehydration while also lowering the risk of hyponatremia (low sodium in the blood), a potentially dangerous condition increasingly seen as runners have erroneously been instructed to over-hydrate."

The American College of Sports Medicine has devised hydration guidelines for those who exercise:

- Drink plenty of fluids during the 24-hour period before an event, especially during the meal prior to exercise, to promote proper hydration before exercise.

- Consume 14-20 ounces of fluid about two hours before exercise to stay hydrated and allow time to excrete any excess water.

- During exercise, drink fluids at regular intervals, usually every 15-20 minutes depending on your sweat rate, to replace water lost through sweating.

- For strenuous exercise lasting longer than one hour, drink liquids that contain 4 percent to 8 percent carbohydrates and approximately .5-.7 grams of sodium per liter of water. This helps delay fatigue and replace what you lose sweating. (Regular sports drinks are formulated for these recommendations.)

- To rehydrate after exercise, drink 16 ounces of fluid for every pound of body weight lost during exercise.

A look at the stages of dehydration:

Mild: Increased thirst; dry lips; discomfort.

Moderate: Nausea; sunken eyes; increased body temperature; difficulty concentrating.

Severe: Weakness; mental confusion; rapid, weak pulse (more than 100 at rest); cold hands and feet; rapid breathing; blue lips; confusion; lethargy; muscle spasms.

To get a better understanding of your hydration needs, factoring in activity, duration, intensity and other information, visit the Hydration Calculator at (click on "Hydration").

Sources:; Beverage Institute for Health & Wellness; Louisiana State University; American Council on Exercise