Environmental Influences on Ultra-Endurance Athletes - Dr. Cotter скачать в хорошем качестве

Environmental Influences on Ultra-Endurance Athletes - Dr. Cotter

Invited Session "Ultra endurance exercise; physiological limitations and performance" Environmental Influences on Ultra-Endurance Athletes Cotter, J.D. University Of Otago As if the extreme stress of ultra-endurance exercise, sometimes with severe sleep deprivation, isn’t enough of a challenge, such exercise is often performed in extreme environments (e.g., Marathon des Sables, Hawaii ironman, transcontinental polar expeditions). The importance of environmental influences on human performance and health is apparent from how readily they can cause impairment or termination of exercise; e.g., via bacteria-induced illness, hypoxia-induced pace reduction or acute mountain sickness, severe hypohydration from lack of water, or trench foot or hypothermia from excessive water. The increasingly popular ultra-endurance sport of open-water swimming, with races up to 25 km, may take place in water of 16°C through to 32°C and thereby cause high physiological and psychophysical strain and impair performance. While absolute performance is typically impaired by environmental stress, relative performance (placing) may be markedly improved for those who are prepared genetically, habitually or technologically – all of these being important but not always possible. Most environments impose multiple stressors, which can have additive effects on human physiology, welfare and success, e.g., the Antarctic plateau, at ~3000 m, imposes cold, mild hypoxia, and lack of water and food, which may act collectively to reduce muscle function. Both exercise and sleep deprivation can impair the regulatory systems that act against environmental stressors, such as thermoregulation against both heat and cold stress, but the functional effects are surprisingly small given the number of processes that are impacted on. An environmental influence, perhaps seldom considered, that has several marked effects on ultra-endurance athletes is gravity. Its muscle-damaging effects caused by prolonged eccentric exercise are intuitively recognisable, but also likely to be modest and self-limiting. The prolonged orthostatic stress of gravity may be less intuitive; it leads to lower-limb oedema and rapid expansion of plasma volume, by a surprisingly consistent and substantial 20-25% in many settings. Yet, orthostatic tolerance is greatly reduced because of diminished baroreflex sensitivity and hyperventilation-induced hypocapnia. Thus, environmental influences are integral to ultra-endurance exercise, and may not all be obvious. They exert a wide variety of substantial effects that can impair performance or health in absolute terms, but also enhance the experience for those who are prepared.