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This 8 page Class Notes was uploaded by Elenora Yost on Sunday October 11, 2015. The Class Notes belongs to PHED644 at Eastern Michigan University taught by WilliamArmstrong in Fall. Since its upload, it has received 39 views. For similar materials see /class/221470/phed644-eastern-michigan-university in Physical Education at Eastern Michigan University.
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Date Created: 10/11/15
PHED 644 Advanced Exercise Physiology 11 LECTURE 10 Environmental Exercise Physiology When considering Environmental Exercise Physiology the following topics are usually considered gt Heat amp Humidity Cold Hypobaric Altitude Hyperbaric Diving Air Pollution VVVV Principles of Exposure to Stressful Environments SOURCE L E Armstrong Performing in Extreme Environments Champaign IL Human Kinetics 2000 1 Human cells organs and body systems are highly organized and are capable of undergoing change 2 Each of earth s extreme environments requires a unique set of adaptive responses Adequate acclimatization to Virtually all of the earth s stressful environments requires 8l4 days of exposure and loss of acclimatization to these stressors occurs in l428 days 3 Humans may lack or have insufficient hereditary abilities to adapt to all of earth s stressful environments 4 Stressful experiences result in personal growth temporary perturbations or permanent deleterious effects People vary in their capacity to respond to challenges danger and threats The determinants of the outcome of stressful experiences will be discussed shortly 5 Different individuals respond to the same stressor with different outcomes the level of strain illness or injury will depend upon the level of tolerance developed immune system competence o age level of physical fitness the numberintensitytype of previous exposure 6 Stressors may have positive effects that allow the individual to meet physical or psychosocial demands successfully Among these are o increased physical stamina o more effective coping styles 7 Physical stressors are strongly mediated by psychological factors Ifthese stressors are not viewed as noxious or alarming they produce smaller or even opposite physiological responses 8 Physiological responses at times can be excessive inappropriate inadequate or disordered e g in ammatory diseases 9 If humans are able to prevent avoid control or respond to a stressor they usually will not become ill or injured 10 Psychological strategies eg coping maneuvers may alter the amount of strain experienced by the individual when exposed to a stressful environment worry fear panic etc v selfassurance selfdeception prayer seeking help of others etc 11 Mediators are biological social and psychological modi ers that act on stressors to alter the level of physiological strain experienced eg genetic de cit in a metabolic enzyme peerparental expectations and personality characteristics 12 Physiological and behavioral changes sometimes occur before a stressor is encountered in anticipation of and in preparation for challenges threats and dangers eg preeventjitters Heat Normal body temperature about 37 C 986 F The body is constantly adapting to changes in air temperature humidity air movement solar radiant barometric pressure and clothing insulation Continuous exercise in a hothumid environment poses a particularly stressful challenge to the maintenance of normal body temperature and uid homeostasis gt decreased ability to lose heat by radiationconvection and evaporation respectively slides l amp 2 Hyperthermia refers to elevated body temperature Core body temperatures above 40 C 104 F can cause disorientation and core temperatures above 42 C 108 F can cause convulsions and permanent cell damage quotTherefore core temperature is just a few degrees away from a value 45 C that could lead to death Common heatrelated problems include o heat syncope o heat cramps o heat exhaustion o heat stroke Heat syncope common symptoms include headache amp nausea treatment requires intake of uids Heat cramps refer to muscle cramps spasms twitching that occur in several locations in the body usually during or immediately following heavy exertion in hot humid weather When they occur stop activity move to a cool shaded area and drink water to replace uids lost during sweating Activity can generally be resumed the next day Heat exhaustion Symptoms include o nausea disorientation o weakness profuse sweating cold clammy skin normal to slightly elevated temperature pallor possible loss of consciousness Treatment o move to a cool shaded area o replace uids o place in shock position feet elevated 1218 in prevent heat loss gain o may require medical attention Activity should be avoided for a day or two until the symptoms have disappeared Heat stroke involves the sudden failure of the thermoregulatory system Symptoms generally no perspiration dry skin skin is red or ushed hot as high as 106 F pulse is rapid and strong victim usually goes into shock and is unconscious Treatment o extreme medical emergency o treat for shock o lower body temperature any way possible o possibility of death can be significantly reduced if body temperature is lowered within 45 minutes o transport to hospital quickly Factors Affecting Heat Injury slide 3 o gender o age o tness level o acclimatization o hydration o enVironmental temperature o clothing o humidity o metabolic rate o wind Gender differences Women appear less tolerant than men o lower sweat rates o higher percent fat gt J heat loss differences are small when matched for the same degree of acclimatization and similar body composition Age quotThe issue of whether aging impairs one39s ability to thermoregulate and exercise in the heat is controversial Recent studies indicate that wellconditioned old and young men show little difference Fitness increased heat tolerance acclimatize faster sweat more earlier onset of sweating Acclimatization When exercising in the heat begin with either low intensity lt50 V02max long duration 60 100 min or moderate intensity 70 V02maxshort duration 3035 min gt increased capacity to sweat J J salt loss A A body r and HR response during exercise Regular exercise in the heat gt decreased body temperature decreased HR response increased plasma volume 10 12 due to increased plasma proteins maintains central blood ow sweating capacity allows the body to store more heat with smaller temperature gain earlier onset of sweating as much as 3fold higher sweat rate reduced NaCl loss in sweat due to increased secretion of aldosterone gt J in electrolyte loss but does not minimize the need to replace water loss 2 reduced blood ow to the skin Hydration cold drinks absorb faster than hot when intensity exceeds 6070 V02max gastric emptying decreases IMPLICATIONS 7 RECOMMENDATIONS Exercise lt1 hr iwater only Exercise gt1 hr isport drink containing Na Cl39 CHO PreExercisei lt1 hr SO130 VOzmax gt1 hr 6090 VOzmax 300 500 ml 30 35 g CH0 300 500 ml H20 1 3 hr 6090 VOzmax 10 20 mEq Nat amp Cl39 68 CHO 500 1000 mlhr gt3 hr 3060 VOzmax 20 30 mEq Na amp Cl39 68 CHO 500 1000 mlhr Environmental Temperature Exercise temperature gt skin temperature gt heat gain itherefore evaporation must compensate Clothing cotton quotwicksquot sweat to the surface for evaporation Humidity interferes with evaporation Metabolic rate core temperature directly proportional to work rate increased work increases heat load and strain on the physiological systems Wind increased air ow passing the body places more air molecules in contact with the skin gt increased convection and evaporation assuming the air can accept moisture Wet Bulb Globe Temperature WBGT quotis a single temperature which is dependent upon air temperature humidity solar radiation and wind velocity and thus represents a composite measure of the impact of the environment on exercising subjectsquot ACSM Guidelines Dry bulb temperature Tdb ordinary measure of air temperature in shade Black globe temperature Tg measure of the radiant heat load measured in direct sunlight Wet bulb temperature wa measurement of air temperature with a thermometer whose mercury bulb is covered with a wet cotton wick This measure is sensitive to the relative humidity water vapor pressure and provides an index of the ability to evaporate sweat WBGT 07 wa 02 TIg 01 Tdb The following colorcoded ags on the race course give the risk of heat stress red WBGT 23280C 73820F high risk amber WBGT 18230C 65730F moderate risk green WBGT lt18 C lt65 F low risk white WBGT lt10 C lt50 F low risk of hyperthermia but possibility of hypothermia Consideration for Exercise o Allow 57 days acclimatization o Recognize the temperature and humidity conditions defer exercise if exercise is in the high risk zone o Avoid exercise in the hottest part of the day Drink uid before during and after exercise The safest and most acceptable uid replacement is plain water o Wear loose clothing o Decrease training intensity monitor HR o Allow for 10 min rest for every 4550 min of activity o Be aware of heat susceptibility obese unacclimatized un t dehydrated previous history of heat problems o Make sure that you are taking in enough salt potassium and calcium in your diet Cold Hypothermia is the result of a higher rate of heat loss compared to heat production Important to protect against heat loss Maintain core temperature Cold air facilitates heat loss in more ways than readily apparent when air temperature is less than skin temperature a gradient for heat loss by convection exists countered by peripheral vasoconstriction and shivering cold air has a low vapor pressure which encourages evaporation of moisture from the skin to further cool the body Hypothermia is in uenced by slide 4 o Insulating factors subcutaneous fat clothing wet v dry 0 Environmental factors temperature water v air the thermal conductivity of water is 25 times greater than that of air slide 5 watervapor pressure wind 0 Energy production increases on exposure to the cold with an inverse relationship between the increase in V0 and body fatness women cool faster than men when exposed to cold water exhibiting a longer delay in the onset of shivering and a lower V02 despite a greater stimulus to shiver Cold however is generally less of a risk during exercise because most people dress appropriately for outdoor activity and aerobic exercise itself generates large amounts of heat Three primary areas of concern are prevention of frostbite and other exposure injuries 2 subjective sensation of symptoms of angina patients Cold air breathing and dramatic skin cooling may make it more difficult for angina patients to discern andor grade their angina symptoms 3 cold may lower the anginal threshold or even cause angina at rest
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