You finally made good on your promise to get fit for the ski season. Now you and your monster quads are ready for that spring ski vacation. But your muscles need more than mass to get through a hard day on the hill. They also need fuel in the form of water, oxygen and nutrients from food. Neglect one—or all three—and prepare to suffer dire consequences.

WATER LOG
Summer plays fair: The threat of dehydration is as obvious as the sweat on your brow. In winter, unseen factors conspire to dehydrate you and undermine your performance and safety.

Simply step out of the car on a powder day and the assault begins. Moisture is plucked from your mouth, throat and lungs with every breath as the body humidifies winter's dry air so the lungs can use it, says Larry Armstrong, University of Connecticut professor and author of Performing in Extreme Environments.

Next, the body's exposure to cold (and also to high altitude) triggers a process called cold-induced diuresis, which raises blood pressure and makes the kidneys work harder, so they produce excessive urine, says Robert Robergs, director of the exercise physiology laboratories at the University of New Mexico.

Perhaps most insidiously, a normally attired skier exercising moderately to heavily at 32 degrees can lose four pounds of sweat per hour, researchers estimate, or 2 percent of a 200-pound male's weight. Merely a 1 to 2 percent loss begins to spur bodily responses, such as increased heart rate.

Perspiring pulls liquid from the bloodstream. If that liquid isn't replaced, blood volume drops and the heart must pump harder to keep that diminished amount circulating. Neurotransmitters then send the brain a message: You're whipped. And it's only, ahem, downhill from there. It is not uncommon for a 150-pound skier to lose three to six pounds of fluids—a 2 to 4 percent loss in body weight—in just three hours on the slopes, physiologists say. Muscle control erodes, and the ability to notice fine detail and control motor tasks diminishes, adds Robergs. "You make one bad decision going down a slope at 45 miles an hour, and it's potentially deadly."
—Chris Solomon

OXYGEN
Anyone who's taken ninth-grade biology knows that our blood carries not only water but also oxygen—which we get from the air we breathe—to muscles and organs that use it as fuel. Decrease the amount of oxygen in your blood, and bodily functions, such as muscle endurance, suffer. Essentially, that's what happens when you ascend to high altitudes (5,280 feet and above).

At 8,000 to 10,000 feet, lower atmospheric pressure makes the air 30 percent less dense than it is at sea level, so each breath delivers about a third less oxygen to your blood, explains Dr. Andrew Subudhi, assistant professor at the University of Colorado Altitude Research Center.

"To compensate, your body's major response is to increase its resting respiratory rate," he says. In other words, you recalibrate your system by taking deeper or more frequent breaths in order to maintain the blood-oxygen levels necessary for your muscles and organs to function.

This process, known as acclimatization, happens automatically, but it takes time. Ascending too quickly or exercising strenuously before your body adjusts (e.g., taking several mogul runs at 11,000 feet the same day you left L.A.) can shock your system and is one of the biggest mistakes skiers make, says Subudhi. Your body uses oxygen faster than your respiratory rate can provide it. Essentially, demand outpaces supply. The result: O2 deficiency—responsible for muscle fatigue and subsequent soreness at best, altitude sickness or hypoxia at worst. Either can turn the first day of your ski vacation into your last.

To ensure your vacation lasts as long as you intend, Dr. Subudhi recommends taking these three steps: First, ascend gradually, perhaps spding a night at an intermediate altitude before heading to the mountains. Second, don't overexert yourself on the first day. Ski a half day or stick to easier terrain until you're fully acclimatized. Third, go easy on the alcohol, which speeds dehydration and can compound the effects of oxygen deficiency.
—Deborah Marks

FOOD FACTS
Experts estimate that a vigorous skier burns up to 4,000 calories per day, so plan to consume from 500 to 1,500 more calories during a full ski day than you would for a day at the office. "Skiing with less than adequate glycogen stores in your muscles can decrease enjoyment and affect fine motor coordination," says Dr. Wayne Askew, director of the Division of Nutrition at the University of Utah and an avid skier. Or you might peter out altogether, especially if you skimp on carbohydrates, warns Kim Mueller, a San Diego–based registered dietician and sports nutritionist. So forget what Dr. Atkins told you and load up on carbs. They're the primary energy source for muscle contractions and the sole fuel for your brain, red blood cells and nervous system.

Consequently, ski-day meals and snacks should be carbohydrate-focused: Aim for four grams of carbs for every gram of protein, Mueller suggests. Small amounts of protein and fat—because they're processed more slowly than carbs—can help you feel full longer. But eat too much and you may find yourself dragging. "If you have a three-egg ham omelet for breakfast or chicken nuggets and fries for lunch, water, blood and oxygen that should be going to your muscles will be diverted to your belly," Mueller says. "That can leave you feeling lethargic and crampy." Watch for the same effect if you gorge yourself at any meal. Instead, spread your calorie consumption throughout the day, using the following approach.

• Before You Go: To build up your glycogen energy stores, fuel up the night before with complex carbs like whole grains and veggies, says Susie Parker-Simmons, a sports dietician for the U.S. Olympic Committee and author of the U.S. Ski Team's Sports Nutrition CD-ROM ($60, educationshop.ussa.org). Then plan to consume 400 to 900 carb-focused calories in the two to three hours before you ski. And check the weather forecast: The colder it is, the heartier your breakfast should be. That's because anywhere from 7 to 20 percent of the energy in food can be liberated as heat when your body converts food to fuel, Askew says. Plus, glycogen boosts your shivering response, which helps keep your temperature up.

• On the Hill: Statistics show that 11 a.m. is the most likely time to get injured on the slopes, thanks in part to skiers who expect their morning meal to keep them revved up until lunch. "Carbs have a limited storage capacity," Parker-Simmons says. "So you need to consistently fuel." She recommends 30 grams of carbs for every hour of skiing. Energy bars, gels or drinks can also do the job; just make sure they're not too protein-dense, and test them beforehand to see how they handle cold. Then fill up with a carb-heavy lunch in the lodge, and stock up on afternoon snacks before you head back to the hill.

• Après-Ski: Once you click out of your skis, hold off on beer and hot tubs: You only have a 30-minute window to jump-start your body's recovery. "After a workout, the body is very responsive to insulin," Mueller says. "You'll replenish your glycogen stores two or three times faster than if you wait to eat." Rehydrate, and shoot for 30 grams of carbs and six to 20 grams of protein, which can help repair muscle damage (read: soreness) more quickly. Good recovery snacks include hot chocolate, cider, energy bars, cheese and crackers, and peanut butter and jelly. At dinner, carbs are still key. Also opt for plenty of fruits and vegetables rich in antioxidants (such as vitamins A, C and E and beta carotene) to counteract destructive agents called free radicals that form in your muscles when you exercise at altitude. "There's evidence that they can come on even stronger after you return to lower altitudes," Askew says. "The worst thing you can do is go home and eat hamburgers and french fries."
  —Kellee Katagi
  
  SAMPLE MOUNTAIN MENU
  
  • Breakfast: Oatmeal with wheat germ, walnuts, berries and vanilla soy milk—or combos such as Special K, milk and a banana; toast, eggs, cantaloupe and juice; or yogurt with fruit and low-fat granola.
  • Lunch: Soup in a bread bowl and a small salad or an apple and warm pasta with moderate amounts of chicken or meat sauce. A small slice of pizza is fine, but avoid fried foods, which can weigh you down.
  • Dinner: Turkey and sweet potatoes or fish, rice and veggies—especially if you're planning to ski again the next day.

  
  —Kellee Katagi
  
   
  
  HOW TO HYDRATE IN WINTER
  
  • 1. Drink preemptively. Studies show that people are already about 2 percent dehydrated by they time they feel thirsty. The American College of Sports Medicine recommends slowly drinking about 17ounces of water one hour before exercising.
  • 2. Sip, gulp, whatever. Experts recommend drinking six to 10 ounces every 15 minutes. Downing half of your Nalgene bottle every half-hour is fine, too—though that sometimes makes people feel queasy. Don't simply fill your tank every three hours, says Robergs—the gut only absorbs about 34 ounces of liquid per hour, and the body needs time to return fluid to the right places.
  • 3. Don't fall off the wagon. A few après-ski margaritas in a hot tub is an American tradition, but they desiccate an already dehydrated body. Weigh yourself before and after exercise, replace the difference with a double agua—not aquavit—and you'll recover faster.
  
  —Chris Solomon