Environment and Exercise Chapter 17

Learning Objectives Know the basic physiological responses to exercise in cold and hot environments. Understand specific elements of acclimatization to cold and hot elements. Know the primary health-related risks of exercising in the cold and heat. Be aware of the potential effects of exercising at altitude on health and performance.

Adaptation to Heat and Cold Maintaining Thermal Balance Sources for gaining heat:  Environment  Metabolism Factors leading to loss of heat:  Conduction  Convection  Radiation  Evaporation

Two Problems in Adjusting to Thermal Environment 1. Heat dissipation in hot climates 2. Heat conservation in cold climates

Temperature Regulatory Center In the hypothalamus Regulates body temperature through receptors Senses body temperature in:  Preoptic area of the anterior hypothalamus  Skin  Some internal organs

How the Temperature Regulatory Center Works Increases rate of heat loss from the body:  Stimulating the sweat glands to secrete  Inhibiting the sympathetic center Increases heat production by stimulation of:  Shivering  Catecholamine release  The thyroid gland

Exercise in the Cold Potentially dangerous outcomes:  Hypothermia  Frostbite Other potential problems:  Trenchfoot  Chillblain  Chilling  Adverse effects to performance in aerobic/ anaerobic activities and in muscle strength

Cold Acclimatization Continued exposure to cold results in greater ability to withstand cold. Long-term cold acclimatization:  Increased basal metabolic rate  Decreased peripheral circulation  Increased body fat

Summary of Exercising in Cold Environments Effects:  Loss of body heat countered by increased metabolic heat produced by activity  Heat dissipation occurs by radiation, convection, and evaporation (through sweating) Risks:  Hypothermia, frostbite, nonfreezing cold injuries Precautions:  Dress in warm clothes and layers; wear dry socks and shoes Acclimatization effects  Increased basal metabolic rate, decreased peripheral circulation, increased body fatness

Combined Effect of Wind and Temperature (Wind Chill Factor) Source: American College of Sports Medicine Position Stand. Prevention of cold injuries during exercise. Med. Sci. Sports Exerc. 38: 2012–2029, 2006.

Exercise in the Heat Can be more serious than exercising in the cold Metabolism and environment combine to increase heat gain in body tissues. When outside temperature approaches skin temperature (92° F), heat loss through convection and radiation end. Sweating becomes the only means of heat loss.

Hot, Dry Environments vs. Hot, Humid Ones Hot and dry:  Cooling of the skin is brought about by sweat  Slow-moving blood in/close to the skin helps transfer heat to evaporative surfaces and enhances cooling  Exercise can impose severe loads on cardiovascular system  Dehydration is possible Hot and humid:  Evaporative cooling is impaired  Metabolic heat accumulates and raises body temperature  Problems of exercising in a hot, dry environment are aggravated

Human Limitations in the Heat Heat stress Heat strain Muscle (heat) cramps Heat syncope (orthostatic dizziness) Exertional hyperthermia Exertional heat exhaustion Exertional heatstroke

Clinical Application Reducing the Likelihood of Heat-Related Illness Education—learn about effects of exercising in the heat Clothing—minimize clothing to provide more skin surface from which evaporation can occur Hydration—keep well hydrated Fitness—avoid heat extremes if you are a novice, are older, or have circulatory/ respiratory disorders

Effects of Age, Gender, and Obesity on Exercising in the Heat Age:  Prepubertal children and the elderly have less tolerance for heat than adults Gender:  Females better tolerate hot, wet climates  Males better tolerate hot, dry conditions Obesity:  Have a poorer capacity for heat dissipation

Heat Acclimatization Heat tolerance can be improved, to some extent, through physical conditioning. Major physiological adjustments of acclimatization to hot environments take 7–14 days.

Summary of Exercising in Hot Environments

Your Perspective Do you prefer to exercise in colder or hotter weather? Why? What are your methods for staying warm or cool while exercising in extreme temperatures?

Clinical Application Reducing Jet Lag Make eastbound flights during daylight hours Make westbound flights late in the day Drink plenty of water Eat light meals and discourage fatty foods Stretch and walk around at regular intervals Maintain a normal schedule as much as possible

Exercise at High Altitudes Lower atmospheric pressures Decreased availability of oxygen to tissues Decreased aerobic power (VO 2 max) Increased effort of respiratory muscles

Altitude Acclimatization Prime area of concern: Altitudes between 5,000 and 10,000 feet Ideally, acclimatization should take place at progressively higher altitudes Or, undertake progressive conditioning program at the same altitude May take several weeks

Exercising in High Altitudes

Your Perspective One cold January day, you see your younger brother going out for a jog dressed only in shorts and a T-shirt. How do you tell him to dress warmly, without sounding like a nagging parent? How do you tell him to be careful when he goes out for a run in hot, humid August weather?

Where to Learn More? Temperature and performance:  www-rohan.sdsu.edu/dept/ coachsci/csa/vol36/table.htm www-rohan.sdsu.edu/dept/ coachsci/csa/vol36/table.htm Athletes and fluid replacement: 