As we settle into winter in Wisconsin, there is no shortage of cold weather activities from which to choose. You might go skiing, skating, snowshoeing, sledding or simply take your walk or run outdoors. The physiological and metabolic impact of cold weather exercise on the body can be intense. The body needs to work harder to perform in a harsher climate and be able to generate adequate heat to keep warm.
“With any temperature, elevation or intensity change, there is always an initial need for more energy,” said Nicole Kerneen, RD, CD, sports and clinical dietitian with the Froedtert & the Medical College of Wisconsin health network. “This energy is pulled from the glycogen in your muscles, which is a form of carbohydrates. Glycogen is our fuel, our body’s power source, and it is stored energy that is available immediately.”
Fuel up consistently
Winter sports can require vigorous exercise that burns hundreds or even thousands of calories. For example, in a day of skiing a person could easily expend up to 2,000 calories. Kerneen recommends starting the day with a hearty breakfast and having a snack every 30 to 60 minutes after the first hour of activity.
“This could be as simple as having a peanut butter sandwich or an energy bar,” Kerneen said. “That’s a snack with enough carbohydrates to re-energize you and enough protein to keep you feeling full and satisfied.”
A study of Navy SEALs participating in mountain warfare/cold weather training found they struggled to keep up with their body’s energy demands.1 The study looked at the SEALs’ energy expenditure and their energy intake and determined that increasing intake, primarily with carbohydrates, during planned breaks and downtime could help. While this is an extreme example, the research demonstrates the importance of regularly replenishing nutrients during periods of physical activity in the cold.
“Your body will fatigue faster in the cold weather without adequate fuel,” said Julie Carpenter, a licensed athletic trainer at the Froedtert & MCW Sports Medicine Center and athletic trainer for the U.S. speedskating team. “The cold slows down all of your body’s chemical processes, including your nervous system’s ability to generate a muscle contraction.”
While physical activity in the cold requires more nutrients, exercising in a cold climate will not necessarily cause an individual to burn more calories than in a temperate climate. Generally, exercising generates enough heat that the body should not have to engage in additional heat-generating mechanisms that burn calories, such as involuntary muscle contractions through shivering or the activation of brown fat cells, dark-colored adipose tissue found throughout the body containing stored energy. The number of calories an individual burns during exercise depends on many factors, including his or her level of physical fitness, height, weight, body composition and age.
Hydrate even when you don’t feel like it
Dehydration during cold weather exercise carries the same risk as it would when exercising in the heat, but a person will not feel as thirsty. The cold diminishes thirst by up to 40 percent.2
“Your blood vessels constrict when you’re cold and prevent blood flow to the extremities, like your hands and feet,” Carpenter said. “Blood vessel constriction is a warming mechanism that allows your body to draw more blood to your core.”
Research published in Medicine & Science in Sports & Exercise found this process of vascular constriction leads to reduced secretion of a fluid-regulating hormone called arginine vasopressin, or AVP, which leads to a decline in thirst.3
Respiratory fluid loss and sweat (which can be less noticeable under winter layers than in the summer) also contribute to fluid loss.
“When you breathe in cold, dry air, your body warms and humidifies that air,” Carpenter said. “When you exhale, the vapor you see is actually fluid loss.”
The speedskaters Carpenter trains are accustomed to pushing their bodies to the limit in cold conditions. While the skaters usually practice indoors at the Pettit National Ice Center, they still have to take into account cold conditions at the rink. They also frequently compete outdoors.
“Whether they are skating indoors or outdoors, most of them wear a scarf over their face or a face mask to prevent dehydration and to keep their airways moist,” Carpenter said. “They also bring warm liquids, like tea, to encourage hydration.”
A good rule of thumb is for every hour of physical activity — in the cold or in the heat — the body needs 16 ounces of water.
Be aware of hypothermia and frostbite
Exercising in cold temperatures can put the body at risk of hypothermia, which occurs when body temperature drops below 95°F. Consider the wind chill when preparing for cold weather activities. Plenty of layers and moisture-wicking clothing are the best defense, along with limiting exposure.
“The body does an excellent job of maintaining a constant temperature, but extended exposure to cold can overwhelm its auto-regulation mechanism,” said Matthew Chinn, MD, emergency medicine physician with the Froedtert & MCW Moorland Reserve Emergency Department. “Shivering is one way the body maintains its temperature. As hypothermia progresses, the body’s shivering mechanism may stop working, people may become confused and the heart can stop working normally.”
Frostbite can cause permanent damage to the body as skin, nerves and tissue freeze at the site of injury. A person’s extremities, such as their hands, feet, ears or tip of their nose are most vulnerable. Frostbite can occur on exposed skin in less than thirty minutes.
“The first signs of frostbite can be numbness, clumsiness and cold skin,” Dr. Chinn said. “The skin can also appear discolored or turn black.”
Gloves, warm socks and hats are good protection from the cold.
To achieve peak athletic performance in cold conditions, research shows that consuming the right nutrients early and often and hydrating even when you are not thirsty will go a long way. Layered clothing to provide insulation and protection from the elements, as well as avoiding extended exposure to cold, will also protect you from certain dangerous conditions.
For more information on improving your athletic performance, visit: froedtert.com/pep.