Running Cold: Your Body Exercising in the Wintery Outdoors

by Ally Gallop

In a city of runners, the past few weeks have made it difficult to train. As the snow begins to (hopefully) melt, many runners are itching to return to the outdoors. Though cleared trails are advantageous, this cold Northeastern weather is not. Knowing how the body deals with the cold will help you train smarter. So what does your body do the moment you step outdoors, ready to exercise?

Your Body Fights to Maintain Its Core Temperature

The human body prioritizes. When the brain senses core temperature dropping, blood vessels are signaled to narrow (vasoconstriction), thereby pulling more blood towards the core. Temperature is therefore regulated, but at the expense of the extremities. The fingers and toes acquire less circulation and become cold, and dexterity is impaired. With the rush of blood being diverted, the steady blood volume tells the brain it’s hydrated and the kidneys continue to produce urine. Yet this is all problematic for the thirst sensation.

In normal conditions, when blood volume decreases the brain tells us to drink fluids. But as described above, cold conditions and blood diversions translate into the thirst sensation being reduced by up to 40%. Again, this relates to prioritization: the body decides that staying warm is of greatest importance. Still, the hydration situation gets worse.

In cold weather, we lose water through breathing. Ever notice that cloud that appears upon exhaling? That’s the moisture in your breath condensing as it meets the colder air. Inhaling cold air requires extra work by the body to warm and humidify it. And even though you may not feel it, you’re still producing sweat. By combining blood diversion, urine output, moisture loss through breathing and sweating, and the reduced sensation to drink, dehydration is an increased and definite risk in cold weather.

Working muscles produce heat and can compensate for it being lost. But temperature regulation still depends on what you are (or aren’t) wearing. Inadequate cold-weather clothing, materials, and layering will have a big impact on how your body reacts. In regards to your base layer, or the clothing directly against your skin, cotton collects sweat rather than wicking it away. Sweat remaining against your skin speeds up heat loss, thereby increasing the risk of chills and shivering (opting not to wear a waterproof shell in the rain has the same effect). In comparison to air temperatures, the body loses heat from wind at a faster rate. The risk of frostbite is below 5% when the wind strikes at 5°F (-15°C). But in conditions under -18°F (-28°C) frostbite can occur in less than 30 minutes.

Where else do we lose heat? A bare head allows for blood to be cooled as it passes through vessels located just below the skin. This is especially apparent in an exposed forehead. Shivering would normally result in involuntary muscle contractions generating heat in the amount of roughly four times that of the resting metabolic rate. But when the head is exposed, even when adequately dressed, shivering won’t occur. Body temperature will drop faster than expected with a heat loss of 30-40%.

As a curious Friedmanite and dietitian, I wondered: where does food fit into all of this? Since the cold leads to vasoconstriction and reduction of blood flow to the peripheries, fat utilization during exercise is lowered. Thus, the body relies heavily on blood sugar and glycogen stores to fuel activity. As glycogen is burned at a faster rate, performance worsens more quickly, the body’s ability to tolerate the cold is decerased, and fatigue occurs sooner. This is why when you feel cold you also feel hungry: eating produces heat (i.e. diet-induced thermogenesis) and provides fuel.

No Excuses: Get Exercising

Now that you know the basics of how the body adapts to the cold, you can train smarter with the following tips:

Tip #1. Layer Your Clothing: One thick sweater isn’t going to cut it—you need to trap that escaping heat, which is best accomplished by wearing layers. Each layer serves a purpose:

  • Base layer: wick the sweat away from your body. Opt for wool or a polyester fabric over cotton. My favorite long-sleeve running top is made by Craft.
  • Middle layer: thin or thick; fleece, down, wool, or a synthetic fabric; it’s really whatever you prefer. Lululemon offers form-fitting layers that don’t impede running strides.
  • Outer layer: go for windproof and waterproof shells. One with a zipper down the front, like this Lolë jacket or an offering from GORE-TEX, easily allows for removal if you become too warm.

Layers allow you to keep warm or strip down, thereby providing options. You’re going to produce heat when exercising, so aim for attire that has you feeling slightly cold at the beginning of a workout. Overdressing increases core temperature beyond comfort and can contribute to dehydration and excess sweat remaining on your skin. Keep exposed skin to a minimum by opting for long sleeves and full-length tights. Runner’s World provides a rough guideline on how to layer depending on the forecast.

Tip #2. Cover Exposed Skin: If frostbite were to occur, the fingers and toes are among the first areas affected. Choose mittens over gloves: mittens create a pocket of warmth around the fingers as a whole; gloves don’t. Choose wool socks to protect your toes from those slush puddles you’re bound to stride in. Decrease rapid heat loss by covering your head with a thick headband, earmuffs, and/or fleece hat. If you have an upper respiratory condition or a history of chest pain, cover your mouth loosely with a scarf or balaclava to allow incoming air to be warmed.

Tip #3. Hydrate and Eat: You cannot depend on the thirst signal. Rather, the American College of Sports Medicine recommends 125 ml (4 fluid ounces) to be consumed every 20 minutes. I stay hydrated with the handheld FuelBelt. No icy fluids, though, as this will lower the core temperature.

If participating in a sport that makes it difficult or uncomfortable to consume solids, gain your carbohydrates though sports gels or fluids. Aim for 30-60 grams of carbohydrates per hour. This equates to 1-2 Powergels or 2-4 cups Gatorade.

Tip #4. Warm Up and Cool Down Inside: Warm up inside without breaking a sweat. Try Runner’s World Magazine’s Winter Prep Workout. Remaining outdoors after exercising will cause body temperature to quickly lower. Get indoors and change into dry clothes immediately.

Tip #5. Stride Safely: Cold weather running is about mileage and maintenance; not speed. Ice, snow, and slush all increase the risk for injury. Pace yourself at a comfortable rhythm and aim for running paths that allow stable footing; for instance, plowed trails or packed snow. Increase traction by attaching Yaktrax to your runners.

Helpful tips are, well, helpful. But it’s trial and error that matters most. Log your runs not only in regards to lap time and mileage, but the temperature, wind chill, what you wore, how you felt, how much fluids and fuel you consumed, and what you would alter next time to make your experience better. It’s your cold weather workout, so personalize it and know your limits.

Ally Gallop, BSc, RD, CDE is studying towards an MS/MPH focusing in nutrition communication and behavior change. She continues to train for the Boston Marathon with Tufts Marathon Team while donning mittens and running along the Charles.

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