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Nutrition with Donna Marlor Fluid guidelines for cold weather endurance training The arrival of my Birkie registration in early August always serves as a motivator to start thinking seriously about a fall training schedule for the upcoming ski season. Time to get disciplined and add some intervals. Make a commitment to set aside a day for over-distance running. Get on the roller skis. And, of course, figure out a way to fit all of this in today with fewer hours of daylight. Getting the most out of training means matching one's metabolic demands with the right nutritional support. Often overlooked by endurance athletes is the effect cooler weather has on hydration needs. Let's take a closer look at what that means. For information, I turned to the U.S. Army Research Institute of Environmental Medicine, a group that has extensively studied the effects of a cold environment on hydration. I asked, via e-mail, institute researcher Robert Kenefick, Ph.D., FACSM, why our sensation for thirst goes down with the mercury in a thermometer. He replied, "We believe this response is due to a change in where the blood is in the body when exposed to cold. As you might know, when exposed to cold, blood goes from the periphery and is redirected to the body's core." The significance of this shifting of blood from the arms and legs to the core is twofold, Kenefick said. One, less heat is lost to the environment, which helps to keep our core temperature warm. The second effect has to do with the increase in central blood volume. "Even when people are dehydrated and have less overall volume, the core body tells the brain that blood volume is OK, that there's less of a need to drink, even despite being dehydrated." My next question was whether reduced thirst in cold weather meant that dehydration was not as serious of a threat in such conditions? Kenefick said he and his colleagues had wondered the same thing. Naturally, that had led to another study. "To try to answer your question, Sam Cheuvront has specifically looked at the impact of dehydration when in the cold, on performance," Kenefick wrote. "Both my work and Sam's show that dehydration in the cold (while not the best situation) has much less of an impact compared to dehydration when in a temperate or hot environment. This would not be the case if at altitude or if dehydration was to be maintained for long periods of time (as in days)." I pored over the details of Cheuvront's study, published in the Journal of Applied Physiology in 2005. The details are important in research, and for the Birkie bound, they can make or break a race. As Kenefick had said, a fluid deficit at cold temperatures did not have as much of an impact in the short term. Again, fluid shifts to the core helped to maintain normal blood volume, which permits the heart to have a normal stroke volume. In other words, your heart is able to pump a sufficient amount of blood per beat to deliver oxygen to the muscles. This is not the case in hot weather, when fluid shifts to dissipate heat result in a significant decrease in core blood volume, and hence, oxygen delivery. It was worth noting that the subjects used in this study were not wearing heavy clothing. In fact, they had on T-shirts, shorts and cotton gloves in a 2-degree Celsius room. The cycling protocol called for 30 minutes at low-intensity effort followed by a 30-minute time trial. None of the subjects in the study suffered more than a 3 percent level of dehydration. In other studies, in which the subjects wore insulated clothing, decreases in performance were recorded. Practical cold weather hydration tips As the seasons change from summer to fall, temperatures moderate and athletes typically relax their concern for fluid intake during exercise. But should they? Peeling off a sweat-soaked T-shirt after a workout is a good reminder that exercise generates a lot of heat. Whatever the temperature, having a hydration strategy for endurance training and competition is essential. Here are some hydration tips: Dress for the weather: Shorter days and weaker sun exposure means cool starts for fall events. There is a tendency to dress too warm for conditions, particularly when races last two to three hours, during which temperatures gradually increase. Layering with clothes that can be peeled off, or a top that zips open can make the difference between losing a couple of pounds of water weight vs. a half a pound. What to wear is as important a decision as what to drink. New fabrics designed to whisk away perspiration will help to minimize hypothermia risk when temps are low, as well as evaporation for effective cooling when the thermometer rises. A training log that includes temperature, humidity and wind can help you fine tune your clothing strategy. Stimulate the drive to drink: When the fog rolls in and the north wind kicks up, a tepid or warmed fluid replacement should be considered. Thirst is decreased in cooler temps, so it is important that beverages be appealing to drink to encourage adequate intake. Chicken broth, hot tea with sugar or a latté can provide needed fluids and be effective for maintaining hydration when alternated with extra plain water. This strategy might provide psychological benefits as well under chilly conditions. Match fluid consumption and beverage choice with exercise intensity: In general, the higher the intensity of exercise, the higher the sweat rate. Ironically, intense exercise slows the absorption rate from the stomach, often causing gastric distress. The key to getting fluids out of the stomach and into the intestine quickly is to choose a hydration drink that has a carbohydrate concentration in the range of 6 percent to 8 percent and composed of a mixture of glucose, sucrose, maltodextrin and fructose. Sweeter, thick fluids empty from the stomach slower. Drinks tasty at rest are often poor choices during exercise, are too sweet and too concentrated, particularly when the pace picks up. Start a race or workout well hydrated: In the rush to take care of other race details, pre-race hydration is often overlooked. The day prior to a race, use the 7-scale color chart to determine hydration status. Ideally, a pale shade of yellow urine (levels 1-3) should result if you've been drinking adequately. (Beer bottle brown is seriously bad news.) On race day, two hours before the event, reach for a sports drink or water and consume 17 to 20 ounces. Ten minutes or less before the race, consume another 10 to 12 ounces of water or sports drink. Make sure you rehydrate post-event: The goal of post-event hydration is to correct fluid loss accumulated during the event. Ideally, this is done within two hours by consuming a combination of water, sports drinks and fruit or vegetable juice. Eating solid food is an efficient way to boost sodium and potassium levels and further increase the urge to drink. Condiments such as catsup or mustard are concentrated sources of sodium and are easily added to sandwiches for a quick sodium boost. Final recommendations Athletes will perform optimally only when well hydrated. Although fluid losses are not as great in a cool environment, clothing, humidity and exercise intensity will be factors as to the degree of water and electrolytes lost during activity. Experiment with fluid intake, delivery systems and fluid choice during training to perform at your best on the day of the big race. Donna Marlor MA, BSN, RD holds a bachelor's of science degree in nutrition and nursing from Northern Michigan University and a master's degree in educational psychology from the University of Minnesota-Duluth. She is a former NMU cross-country ski team member and still enjoys competing in skiing and running at the master's level. Marlor resides in Marquette, Michigan, with her husband and chocolate Lab and can be reached via www.DonnaMarlor.com.
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