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Chapter 17

Chapter 17. Environment and Exercise. Only 15 to 40% of energy is converted into useful work. 60 to 85% of energy is wasted as heat energy. Heat energy must be dissipated or body temperature will increase. In cold climates, the heat produced may not be sufficient to maintain body temperature.

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Chapter 17

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  1. Chapter 17 Environment and Exercise

  2. Only 15 to 40% of energy is converted into useful work. 60 to 85% of energy is wasted as heat energy. Heat energy must be dissipated or body temperature will increase. In cold climates, the heat produced may not be sufficient to maintain body temperature. Heat and Human Physiology Visit the Environmental Physiology Lab www.jsc.nasa.gov/sa/sd/facility/labs/EPL/epl.htm

  3. Regulation of body temperature is brought about by • The temperature regulatory center in the hypothalamus • Receptors sense the body temperature at the • Preoptic area of the anterior hypothalamus • The skin • Some internal organs

  4. How the body looses heat • Conduction • Heat exchanged via physical contact • Convection • Heat transferred by a moving fluid • Radiation • Heat transferred by electromagnetic waves • Evaporation • Heat transferred by changing liquid to gas

  5. Temperature regulatory center • Increases heat loss from the body by: • Stimulating the sweat glands to secrete • Inhibiting the sympathetic center in the posterior hypothalamus • Increases heat production by stimulation of: • Shivering • Catecholamine release • The thyroid gland

  6. Potential problems when exercising in the cold • Hypothermia: severely reduced core temperature • Frostbite: crystallization of fluids in the skin or subcutaneous tissues • Chilling: sudden change in temperature • Adverse effects on performance in maximal and submaximal aerobic exercise, anaerobic activities, and muscle strength Visit Temperature and Performance www-rohan.sdsu.edu/dept/coachsci/csa/vol36/table.htm

  7. Clothes for exercising in the cold • For activities that change in intensity • Clothing that is comfortably warm during warm up • Clothing that can be partly removed during exertion • For vigorous activities • Light-weight clothing to allow passage of sweat • For activities that are less physically active • Torso protection to preserve core temperature (e.g. down vest)

  8. Cold acclimatization • Long-term cold acclimatization involves: • Increased basal metabolic rate • Decreased peripheral circulation • Increased body fat

  9. Exercising in cold environments

  10. Wind chill and exercise • -20 degrees F with no wind unlikely to cause frostbite • -20 degrees F with 5-20 mph wind increases danger of frostbite • Vigorous exercise would require tenfold increase over resting metabolism to maintain thermal balance if temp is -4 degrees F with a wind of 9 mph

  11. The combined effect of wind and temperature (wind chill factor)

  12. Problems with exercise in the heat • Metabolism and environment combine to increase heat gain in body tissues • Heat loss through convection ends • Radiation and convection reverse direction and add heat to the body • Sweat becomes only means of heat loss

  13. Effects of exercise in hot, dry climates • Increased volume of slow-moving blood in and near the skin transfers heat to evaporative surfaces, cooling internal environment • Heart rate increases as venous return to the heart and stroke volume is impaired by vasodilation

  14. Effects of exercise in hot, humid environments • Decreased evaporative cooling because evaporation cannot take place • Increased cardiovascular load • Possible dehydration

  15. Guidelines for fluid replacement in the heat • Weigh in without clothes before and after exercise. For each pound of weight lost, drink two cups of fluid. • Drink a rehydration beverage containing sodium as well as 6 to 8% glucose or sucrose. • Drink 2.5 cups of fluid two hours before the activity. • Drink 1.5 cups of fluid 15 minutes before the activity. • Drink at least one cup of fluid every 15 to 20 minutes during activity. • Do not restrict fluids before or after the event. • Avoid beverages containing caffeine and alcohol. Visit Nutrition and the Athlete: Fluid Replacements www.ianr.unl.edu/pubs/foods/nf72.htm

  16. Heat-related illnesses • Heat stress • Heat strain • Heat exhaustion • Heat stroke

  17. Factors that can reduce likelihood of heat-related illnesses • Education • Clothing • Hydration • Fitness

  18. Other factors to consider regarding exercise in the heat • Age • Gender • Obesity

  19. Heat acclimatization • Heat tolerance can be improved to an extent by conditioning alone • Improve function of sweating mechanism • Expand plasma volume • Increase sensitivity to sweating response • Major physiological adjustments of acclimatization to heat take 7 to 14 days to occur

  20. Exercising in hot environments

  21. Exercise at high altitudes • Decreased VO2 max resulting from • Reduction in oxygen saturation of arterial blood • Higher cost of increased lung ventilation • One-maximal-effort activities such as shot put, long jump, and high jump do not depend on oxygen and are unaffected • Events of less than one minute are also unaffected, but recovery takes longer • In events lasting two minutes or more, performance losses of 20 to 30% may be expected without acclimatization Visit The High Altitude Medicine Group at www.high-altitude-medicine.com

  22. Altitude acclimatization • Increase altitude systematically • Undertake progressive conditioning program at the same altitude at which progressively increasing demands gradually improve cardiorespiratory endurance • Acclimatization can take weeks or months Visit OA Guide to High Altitude: Acclimatization and Illness at www.princeton.edu/~oa/safety/altitude.html

  23. Physiological changes of altitude acclimatization • Increases in: • Red blood cell count • Hemoglobin content in the blood • Plasma volume • Lung ventilation • Aerobic enzyme activity • Capillary density • Mitochondrial density in skeletal muscle

  24. Exercising in high altitudes.

  25. Using oxygen at high altitudes • Supplemental oxygen essential during work at high altitudes of 18,000 to 20,000 feet or more for most people without a long acclimatization period • Oxygen shortens recovery times at altitude

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