As mentioned in the introduction most of the energy liberated during physical exercise is converted to heat. Depending on the metabolic rate, the prescriptive zone and upper and lower critical temperature shifts (see Fig. 2.3.4) and the physiologic mechanisms for heat loss and heat conservation are taxed to varying degrees, depending on how the heat balance is attained. Therefore, some benefits for exercise and performance are obtained in cooler environments. In submaximal cycling at ambient temperatures of 4, 11, 21 and 31 °C, the time to exhaustion was longest at 11 °C and shortest at 31 °C, demonstrating that the effect of ambient temperature on exercise capacity follows an inverted U-shaped relationship . This study demonstrates that exercise capacity is greater in low suprazero ambient temperatures than at higher temperatures, where the physiologic load on the circulatory system is higher. The ambient temperatures in winter sports are usually below the freezing point and evidently the best conditions for prolonged high intensity physical activity prevail close to but above zero. Optimal performance must therefore be obtained by choosing the proper clothing.
The deleterious effects of cold on performance are manifested on two levels. The more common is the effect of peripheral vasoconstriction and cooling, which lowers the temperature in the tissues, e.g. in hands and feet. The rate of the physiologic and chemical processes is then slowed down, including the rate of muscle contraction and nerve conductivity. Furthermore, stiffness in tendons and connective tissue is increased. This leads to clumsiness and increases the risk for injury (Fig. 2.3.7). Thus, for winter sports competitions warming up is of great importance.
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