Washington ? Ever wonder why an outdoor workout in cold weather doesn’t leave you gasping for the water bottle nearly as much as a similar summer exertion? Well, sidle up to the water filter and draw yourself a tall cool one, folks. It’s biology lesson time.

First: Your body loses, and needs to have replenished, just as much fluid when it’s cold outside as it does in the heat. You sweat just as much in the cold, but the dry air laps up the moisture before it can pool on your skin. The only difference is that you feel less thirsty in the cold, and that can be dangerous.

Why the repressed thirst? When your body senses cold air, blood vessels constrict, pushing blood to the body’s core to preserve heat, explains Robert Kenefick, associate professor of exercise science at the University of New Hampshire.

“If your body kept that heat near the skin when there was a big temperature differential between the air and your body, you would lose heat quickly to the environment,” said Kenefick, whose study on cold, hydration and thirst was published in the September issue of the journal Medicine & Science in Sports & Exercise.

The blood concentration inadvertently fools your thirst-regulating mechanism into thinking that the body has ample fluids. Your hypothalamus, sensing all that blood in your belly, thinks you have plenty of juice. So: No call for the beverage cart.

Regardless of whether you’re walking, hiking, running, bicycling, skiing or whatever, you are likely to feel less thirsty than you would doing the same thing in warm weather.

So, despite a lack of thirst, do the same things you’d do in warmer weather: Shoot for 17 to 20 ounces of water about two hours prior to exercise and, if possible, five to 10 ounces every 15 to 20 minutes during exercise. Afterward, drink 24 ounces for every pound of lost body weight.