Although mild to moderate work and routine physical training typically result in whole-body sweat losses of L/h, the highest sweating rate ever reported for an athlete wasL/h, in conjunction with the marathon of the Summer Olympic Games. Further, we know that the maximum amount of fluid that empties from the stomach during exercise is L/h in most athletes. This explains why athletes routinely experience a – loss in body weight during competition and training.
Previous publications have examined the impact that dehydration has on muscular strength. These articles, written by respected physiologists indicate that it is unlikely that small or moderate reductions in body weight due to dehydration – to – alter strength.
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In fact, dehydration to – or more can be tolerated without a loss of maximal strength. However, sustained or repeated exercise that lasts longer than seconds deteriorates when moderate to severe dehydration exists – or more. This probably results from reduced muscle blood flow, waste removal, and heat dissipationall of which are necessary for high-powered, sustained muscle action in events such as boxing, judo, and pursuit races in velodrome cycling.
In contrast, there is little doubt that acute dehydration, or its long-term counterpart chronic hypohydration lasting or more hours without rehydration, degrades endurance performance, regardless of the environmental temperature or whole-body hyperthermia. For example, maximal oxygen uptake V max, a critical component of successful endurance performance, is reduced significantly following moderate body water losses – of body weight in a cool environment. In a hot environment, small to moderate levels of dehydration – to – result in a large VOmax decline. Similarly, endurance capacity exercise time to exhaustion is reduced more in a hot environment than in a cool or mild one. Tabledemonstrates the impact that dehydration has on endurance performance. This summary of previous investigations shows that increasing dehydration column interacts with air temperature column to reduce both VOmax a physiological measurement and endurance capacity a performance variable. You will recall from the previous section that weight losses of – to – had little effect on strength output. These observations coincide with the fact that decreases of plasma volume during prolonged exercise are greater in a hot versus a mild environment. They also suggest that changes in cardiovascular function decreased cardiac output contribute to the decline in endurance capacity shown in table..
Combating Hyperthermia and Dehydration.
In light of the facts above, every athlete, laborer, or soldier should develop a plan to minimize the stress of living, working, training, and competing in hot-humid conditions. If this is not done, decrements in physical performance will be inevitable. The focus of this plan should be to minimize the effects of hyperthermia and dehydration.
Heat acclimatization greatly enhances contestantschances of completing the Marathon de Sablesa -mile foot race across the Sahara Desert.