Monday, February 18, 2008
Effects of dehydration on performance
We all need water. In fact, the human body can only live about one week without water. Our bodies are compromised of 55-75% water, and there is water in all the foods we eat. With such an abundant substance around us, it’s amazing to think that anyone could become dehydrated, but it does happen frequently, and especially during exercise. So why exactly is water so important? What does it do for us and why do we need more of it when we increase our physical activity?When exercising, you may believe that you have more energy to do the given workload when you drink water throughout your workout. This may cause you to wonder if it was just your psyche tricking yourself into thinking that you could do more, or if your body really could do more physiologically. The truth is water is more physiologically beneficial than most people think. One of water’s primary functions is hydrolysis, which is to break a chemical bond with water. During exercise, this is extremely important because water allows your body to break down adenosine triphosphate (ATP) into adenosine diphosphate (ADP), inorganic phosphate, and energy. This energy produced is the energy that is required not only for muscle contraction, but also for digestion, nerve transmission, circulation, building new tissue and gland secretion. Without water, ATP could not be broken down, and these reactions could not take place. Water is also needed for thermoregulation, or the maintenance of body temperature. Your body is warm-blooded, meaning it regulates itself to stay at a specific internal temperature despite the external conditions. This means that when it’s cold, your body reacts in certain ways to stay warm inside, and when it’s hot, it reacts in other ways to stay cool internally. When your body is in a hot environment, the brain initiates the sweating response. The pores on your skin open and release sweat, which is composed of water and sodium chloride. When your sweat evaporates, your body is cooled. It is important to note that without evaporation, your body cannot cool itself down. The primary implication of this is that it is more difficult to thermoregulate in humid conditions, because the sweat cannot evaporate very well. Because internal body temperature rises during exercise and requires perspiration to cool off, water is even more vital during exercise than normal daily activities.The majority of dehydration problems occur at 2-6% body weight loss. For the typical 150 pound person this means a weight loss of as little as 3 pounds in a single exercise session, which is fairly common. The problems that arise with this kind of weight loss include impaired athletic ability and reduced muscle endurance and strength. However, if more than 6% of your body weight is lost, you are at risk for heat cramps and heat exhaustion. In more severe cases, the athlete could suffer heat stroke or even death. Some signs of heat illness include irritability, headache, weakness, dizziness, cramps, nausea, and decreased performance.Water is also essential for fat metabolism. The process by which the body burns fat is called beta-oxidation. Water is used during an important step of beta-oxidation and without it, this process could not be completed. It is very important then for those who are trying to lose weight to refrain from dehydrating themselves just so that the number on the scale looks smaller. The weight lost during a single bout of exercise is nearly 100% water, so don’t try tricking yourself into thinking that it’s all fat loss. You cannot burn fat without water, and fat metabolism will be limited in a dehydrated person.During exercise, your body gets rid of water via perspiration, as discussed earlier. As your body loses water, the volume of blood plasma in the body decreases, and the heart has to beat faster to keep the blood moving to the working muscles. This causes the stroke volume, or the amount of blood ejected from the heart per beat, to go down. Finally, the overall effect on the heart is that the cardiac output, or amount of blood ejected per unit of time, also decreases. This, in turn, decreases the efficiency of the heart and requires it to work much harder to maintain adequate blood flow to the muscles and vital organs. In a severe circumstance, this could lead to circulatory collapse. So how do we become adequately hydrated? Science doesn’t always agree on how much water should be consumed daily, although the range is anywhere from 1-8 liters per day, depending on a person’s activity level. When exercising, however, there is a good rule of thumb to follow. Drink 17 ounces of water 2 hours before the activity and weigh yourself right before you exercise. While you exercise, drink 6-10 oz. every 15-20 minutes. This may seem like too much at first, but this is the amount needed to insure proper hydration. For some people, this may even feel uncomfortable because it’s more fluid than they’re used to having in their stomach during exercise. If this is the case, increase your water consumption gradually -- people can become “better drinkers”. The last step is to weigh yourself after the activity, and for every pound lost during exercise, drink 1.5 pints of water. This will not only replace fluid lost by perspiration, but will insure that the fluid lost as urine will be replaced as well.Some people prefer to drink a sports drink to hydrate themselves because they prefer the taste. This is perfectly fine, and some drinks even have salt added to them, which stimulates thirst, making them drink more fluid and thereby staying more hydrated. The addition of salt also helps replace the sodium lost in perspiration. However, a sports drink is not required for most physical activity, although it is recommended for exercise lasting longer than 45 minutes, or of a high intensity. The ideal carbohydrate concentration of the fluid should be 6-8% and certainly less than 7% if the exercise performed requires a high amount of fluid to stay hydrated. Fruit juices, carbohydrate gels, and sports drinks with a carbohydrate content over 8% are not recommended as the sole beverage during exercise. Furthermore, beverages containing caffeine, alcohol, and carbonation should not be used during exercise as they can stimulate urine production, cause gastrointestinal discomfort, or decrease voluntary fluid intake.Most of us could probably do better at staying hydrated during exercise and even during our daily living. Don’t drink only when you’re thirsty, as this will not insure adequate hydration. If you struggle with drinking enough water throughout the day, try to drink even when you do not feel thirsty. When you feel hungry, first drink some water, as thirst is often disguised as hunger. Another strategy is to always have water available to drink. Many individuals find that it is easy to drink enough when the water is in front of them. Remember, as you improve your hydration, you will be able to perform better as an athlete and your body will be able to stay healthy and strong. Staying hydrated is about much more than simply satisfying your thirst, it’s about enabling your body to be as healthy and fit as possible. So drink up!