Optimize Winter Hydration

Nordic skiers need adequate hydration to train and perform at the highest level. If you are dehydrated, you have less blood volume. Less blood volume means cardiac output - or the amount of blood the heart pumps out with each beat - is reduced. This means oxygen in the blood, is delivered less efficiently to the exercising muscles and your ability to run, ski or cycle efficiently is impeded. Exercise performance is impaired by losing as little as 2% of your body weight through dehydration.

Dehydration is common in the summer but can also happen in the winter. This is because the colder the air, the less humidity it can contain. We lose more fluid as vapor in the air we exhale. We might sweat more too because we are wearing more clothing and our sweat evaporates at a higher rate in dry air. One interesting phenomenon not well known, is that we can dehydrate with less awareness in the winter, as we may not feel as thirsty as we do in the summer.

Dr. Robert Kenefick, an associate Professor of Kinesiology at University of New Hampshire, has studied sports hydration extensively. He found that dehydration can easily occur while working out in the winter, especially if you train outside for hours Nordic skiing. He says winter dehydration can go undetected because physiological changes in fluid metabolism caused by exposure to the cold, actually suppress the sensation of thirst.

Kenefick explains in an article published in Medicine and Science in Sports and Exercise, that fluid balance relies on the stimulation of thirst caused by the loss of salt and water through sweat evaporation and urination. When we get dry, the brain secretes fluid- regulating hormones that make us want to drink and tells our kidneys to conserve more water, slowing urine production. This system is altered with exposure to the cold. When the body becomes chilled, blood is shunted from the limbs to the core of the body to preserve warmth. This shift causes increased fluid volume in the core of the body but decreased fluid volume over all. Kenefick says because the core fluid volume is increased, the overall decrease goes undetected by the brain and there is decreased, instead of increased secretion of the fluid- regulating hormone. The sensation of thirst can be diminished up to 40% and the kidneys conserve less water. We can dehydrate before we know it!

So, the answer to preventing winter dehydration is to drink before, during and after working out. Weigh yourself before and after a long, outdoor work out and replace weight lost with fluid. A pint of water weighs one pound.

That said, hydrating while training outdoors in the winter is not as easy as it is in the summer. No outdoor drinking fountains function in the winter so we have to carry fluid while we train. One of the biggest problems ensuring adequate winter hydration is how do you keep fluid from freezing?!

Here are some tips!

• Warm the liquid before you start exercising.
• Carry a sports drink. These drinks contain sodium and other electrolytes and will stay in a liquid state longer than water.
• Use an insulated water bottle.
• Stow your water bottle upside down. This keeps the fluid at the top from freezing first.
• Put your bottle belt under your jacket to keep it warm longer.
• Use chemical heat hand warmers around the bottle in combination with an insulating sleeve or wool sock.

About the author... Dr. Marie-Christine Leisz is a Sports Physical Medicine and Rehabilitation Physician at Courage Kenny Running and Endurance Sports Injury Clinic. United Hospital