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Alex "Iron Doc" McDonald: Training and Racing in the Heat vs. the Cold
By Alex M. McDonald, MD
8/1/2008 |
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As athletes we all know that there is a big difference between racing and/or training in hot humid conditions versus cold dry conditions. Some athlete are better able to tolerate either extreme while some do better in only one type of climate. This article will explore, from a physiologic perspective, how the body responds to different race day, or training day conditions, as well as give some practical advice on how to make the most of what the weather brings.
Several studies have shown and it is relatively well accepted that an athlete’s VO2 Max (the maximum amount of oxygen that the body can deliver to and be utilized by working muscles) is directly affected by core body temperature. As the temperature rises VO2 Max has been shown to fall. Conversely, to a certain point as the core body temperature is lowered, VO2 Max increases. This demonstrates the importance of keeping the core body temperature in a narrow range for optimal athletic performance.
Additionally, several studies have demonstrated that repeat endurance efforts can be sustained at a higher level as well as improved recovery between sessions when cold water immersion therapy is utilized. Although the exact mechanism behind this phenomenon is unclear, it is believed to be at least in part due to the effects on the core body temperature as well as peripheral muscle and vascular changes. This is why you may have seen some of the athletes in the Tour de France wearing “cooling vests” or “ice vests” before the individual time trial stages. To have an affect on VO2 Max any cooling effort must lower the core body temperature, not just the peripheral skin temperature. Several studies have examined the effect of wetting the skin during exercise and demonstrated no effect on core body temperature, heart rate, oxygen consumption, perceived exertion, sweat loss, or percent change in blood volume in both humid and dry conditions. Despite this scientific evidence, many athletes do report a lowering of perceived exertion with wetting the skin with cool water. However, the best practice way to lower core body temperature appears to be simply drinking cold water.
There are indications that a person’s fitness, as measured by VO2 Max, as well as their body size may have influence on the amount of heat or cold stress that their body can handle. Some studies have shown that, more fit individuals as well as athletes with a lower body mass index may have a thermal advantage when exercising in conditions in which heat-dissipation mechanisms are at their upper limit. Some studies indicate that lighter runners produce and store less heat at the same running speed; hence they can run faster or further before reaching a limiting core body temperature. This is mostly likely due to the ratio of body surface area to body volume, smaller individuals can simply dissipate heat faster, however, the inverse may be true in cold conditions. A larger individual may be better able to maintain their core body temperature longer in cold conditions than a smaller person.
There is conflicting evidence on whether heat acclimatization makes a difference with respect to thermoregulation and the percentage of VO2 Max an athlete can sustain in hot or cold conditions. Although an individual’s VO2 Max will be lower in the heat, some studies have shown that heat acclimatization does not have an effect on an athletes ability to regulate their body temperature. However, there has been some evidence that indicates a cardiovascular benefit after heat acclimatization, indicating, that the percentage of VO2 Max an athlete can sustain in a hot race environment, is greater after heat acclimatization. There is little data examining the physiologic effects of acclimatization to cold temperatures. That being said, many athletes feel they perform better racing in the conditions in which they are accustom to training.
Acclimatization to the heat or the cold will most likely improve exercise performance for numerous reasons. Aside from the physiologic parameters mentioned in the prior paragraph, psychosomatic responses (the mind body connection) and adequate nutrition and hydration strategies that result from acclimatization can have major impact on race day. The heat or cold can make a huge effect on an athlete’s mental focus and execution during a race. We all know the importance of our thoughts during a race, often endurance events are a battle of mind vs. body as opposed to athlete vs. athlete. If race weather conditions are different then an athlete is accustom, doubts about athletic abilities, preparation and fortitude begin to cloud mental focus. A particular study tested individuals physiologic and cognitive performance using a series of measures in 3 different conditions, (1) at baseline, (2) in hot condition prior to and (3) in hot conditions after 10 days of heat acclimatization. As you might expect, is the un-acclimatized cognitive test, individuals performed worse than their baseline under the increase physiologic heat stress. In the acclimatized test their cognitive performance was back at their baseline, under the same physiologic heat stress. As is evident from this study, training in race like conditions may well give an athlete a mental advantage over another.
Secondly and possibly more importantly a well prepared and practiced nutrition and hydration plan can make the difference between a PR and a DNF. The climate can have major influence on an athlete’s sweat rate as well as carbohydrate absorption and utilization. In warmer conditions muscle glycogen utilization is increased, however, gut carbohydrate absorption is decreased. As a result it may be more difficult to maintain adequate blood glucose levels to given exercise at a certain percentage of VO2 Max. As a result it may be a prudent race day decision, particularly in endurance events lasting greater than 4 hours to slow effort and pace a little to maintain adequate carbohydrate ingestion and blood levels to avoid “bonking.”
An athletes hydration and sodium needs can vary greatly due to changes in sweat rate given different weather conditions. It is vital to practice race day nutrition and hydration in training and doing so in the climate expected on race day will help an athlete to perfect their nutrition plan. That being said, it is important to determine your sweat rate in a variety of climates and conditions so that you can properly hydrate on race day regardless of what conditions present themselves. Lastly, training in conditions similar to race day will help you with practice small decisions as well, such as what clothing you may need or if you need additional clothing initially that you can dispose of later in the day.
This all very interesting information and very little of it has actually been proven to be one-hundred percent true all the time, however, it can lead us to some practical recommendations:
- Hydrate before exercise with cool liquids in the heat. This will help lower the core body temperature. Additionally, the more topped off the fluid store are, the more reserve an athlete will have before they reach the point where athletic performance will suffer.
- Determine your sweat rate in a variety of conditions
o Hydrate often with cool liquids in the heat, has been shown to help reduce the core body temperature.
o Continue to hydrate in the cold. Even in cold or rainy conditions an athlete continues to sweat, although at a lesser rate, and must still recoup the fluid losses.
- Get wet in the heat. Wetting the skin and hair has not been show to have any physiologic benefit, although it many athletes swear by it and it simply feels good.
- Considering slowing your pace at time to ensure appropriate carbohydrate ingestions, particularly in hot, humid conditions.
- Train in the conditions you expect on race day. The benefits of heat/cold acclimatization are both psychological and practical.
Exercise in the heat results in major alterations in cardiovascular, thermoregulatory, metabolic and neuromuscular function. Core body temperature appears to be the key determinant of exercise performance and maintaining this temperature in the optimal range will contribute to enhanced exercise performance. Such strategies include heat acclimatization, pre-exercise cooling and fluid ingestion which have all been shown to result in reduced physiological and psycho-somatic strain during exercise in the heat and improved performance.
Alex M. McDonald, MD, is a professional triathlete, coach and a member of the Timex Multisport Team. His interests lie in coaching endurance athletes, sports medicine and exercise physiology. He obtained his MD degree from the University of Vermont. Prior to medical school, Alex graduated from Connecticut College in 2003 with an emphasis on both the biological and social sciences. He currently lives and trains in Durham, NC.
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