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KIN321 Week 7&8 Class Notes

by: askcch

KIN321 Week 7&8 Class Notes 321

Marketplace > University of Miami > Kinesiology > 321 > KIN321 Week 7 8 Class Notes
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Thermoregulation I & II
Introduction to Systemic Exercise Physiology
Dr. Kevin Jacobs
Class Notes
KIN321, SystemicPhysiology
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This 8 page Class Notes was uploaded by askcch on Saturday October 15, 2016. The Class Notes belongs to 321 at University of Miami taught by Dr. Kevin Jacobs in Fall 2016. Since its upload, it has received 3 views. For similar materials see Introduction to Systemic Exercise Physiology in Kinesiology at University of Miami.


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Date Created: 10/15/16
KIN321   Class     otes   Week   7&8   (10/3­10/14)  ________________________________________________________________________________  From    revious  ections  ­ Pulmonary Anatomy and Physiology  ­ Acid­BaseBalance  ________________________________________________________________________________  Lecture 11 Thermoregulation I  ● Heat Production  ○ We are capable of producing a lot of heat during exercise  ■ During intense exercise (80-90%VO2max), 20min to life threatening, 40min to  death if no heat lost to environment   ○ We are better at producing heat than to get rid of them   ○ A majority of produced heat is transferred to the core by convective ow of venous  blood, while small portion is lost to environment   ● Heat Exchange  ○ Radiation, conduction, and convection are driven by temperature gradient (from  hot → cold) → less eective means of heat loss with increasing ambient  temperature  ○   ○ Radiation → infrared exchange of heat with environment  ■ 60% of heat loss at rest in neutral environment  ○ Conduction → Exchange of heat with objects in contact with skin  ○ Convection → Exchange of heat with surrounding air or water  ■ Eectiveness improved by movement of air or water  ○ Heat loss to environment via evaporation  ■ 25% of heat loss at rest in neutral environment   ■ Evaporation of sweat from skin surface  ● Sweat needs to evaporate o the skin, cannot be wiped/dripped o  (no heat loss)  ■ Vaporization from respiratory passages  ■ Only mean of heat loss when ambient temperature greater than skin  temperature  ■ Major mechanism of heat loss  ■ Evaporation inuenced by:  ● Relative humidity and ambient temperature  ● Surface area exposed  ● Convective air currents  ■ Counterproductive sweating → water loss without cooling in hot, humid  environment   ○   ● Temperature Measurement During Exercise  ○ Deep-body (core) temperature  ■ Rectal, tympanic (ear), esophageal, and stomach (pill)  ○ Skin temperature  ● We over produce heat, and we are bad at losing heat   ● Thermoregulation  ○ Hypothalamus = thermostat → protect from heat loss and heat gain  ■ Heat loss mechanisms → Vasodilation + increased HR + sweating  ■ Heat conservation/production mechanisms → Vasoconstriction + shivering   ■ Cold-induced phase vasodilation: keep core temp +  maintain peripheral tissue temp  ● Exercise in the Heat  ○ Two competing cardiovascular demands:  ■ Oxygen and nutrient delivery to skeletal muscle  ■ Heat delivery to the periphery for cooling  ○ Plasma volume decrease during exercise in the heat → increased blood pressure +  sweat loss (sweat is derived from plasma)  ■ Decreased venous return → increased HR to maintain cardiac output  ● Dehydration → ^HR  ○ Sweat rate highly related to exercise intensity → may be as high as 1.5-2.0 L/h in  unacclimatized situations  ● Acclimatization (repeatedly exposed to heat → make body more ecient to get rid of  heat)  ○ Eects:  ■ Lower sweating threshold → pre-emptive (start sweating sooner, get a jump  start on heat loss)  ■ Increased sweat rate → approximately 4 L/h compared to 1.5-1.8 L/h  ■ More dilute sweat → less electrolyte loss  ■ Increased plasma volume → greater sweating capacity, maintenance of  stroke volume and HR  ■ Decreased skin blood ow  ○ Acclimatization is fairly rapid  ■ Majority of adaptations develop in rst week, then more slowly in week two  ■ Plasma volume and HR changes most rapidly, while increased sweat rate  may take 14 days  ■ Two weeks of acclimatization is needed to optimize aerobic performance in  hot ambient conditions  ○ To induce adaptations you must create heat stress → increase core and skin  temperatures until profuse sweating evident  ■ Likely need to reach core temp of ~ 38.5 C  ■ Heat stress from environment + heat stress from exercise = rapid  acclimatization  ■ Gradual loss of adaptations if you remain active when heat exposure is  reduced  ○ Heat acclimatization in dry heat improves exercise performance in humid heat and  vice versa  ○ Training in articially hot indoor environment will induce some adaptations  ■ Outdoor training always considered optimal for preparing for competition  ○ Individual dierences in rate of heat acclimatization exist  ■ Heat acclimatization should take place 1-2 months prior to event  ■ Monitor signs of heat acclimatization including: (during standardized  submaximal exercise bout)  ● Decreased HR  ● Increased sweat rate  + ● Decreased sweat Na content   ● Reduced core temperature  ● Dehydration  ○ Dehydration is dened as %loss of body weight  ■ 5% dehydration → discomfort, loss of appetite, fatigue  ■ Greater than 7% dehydration extremely dangerous  ● 10% → Discoordination, spasticity  ● 15% → Extreme delirium, diculty swallowing   ● 20% → Skin cracks and bleeds  ○ Thirst is not a reliable sign of uid need → drinking to thirst results in body water  decit of 2-3% body weight when exercise in warm-hot environments + high sweat  rates  ■ Need to drink ahead of thirst, BUT DON’T OVER DO IT  ○ Moderate dehydration decreases aerobic capacity & performance  ■ 2% body weight loss → 10-20% reduction in VO2max, 3-5% reduction in long  running  ■ 4-5% body weight loss → 30-50% reduction in VO2max  ○ Fatigue during prolonged exercise may be as much from dehydration as substrate  (CHO) depletion  ○ Primary reasons for decreased performance with dehydration are:  ○               ________________________________________________________________________________  Lecture 12 Thermoregulation II  ● Cardiovascular Stress in the Heat  ○ More cardiac output to skin in a hot environment (to reduce core temperature)  ● Heat Injuries  ○ Heat exhaustion → rapid weak pulse, hypotension, faintness, profuse sweating   ■ Acute plasma volume loss + concurrent vasodilation to skin and active  muscle → low BP  ■ Normal to slight elevation of core temperature (>39.5 C) o ■ Alleviated by rest in cool environment and uid replacement for next 24h  ○ Heat syncope → loss of consciousness with cessation (at the end) of exercise in the  heat  ■ Independent or secondary to heat exhaustion  ■ Happens due to dropped perfusion to the brain (because lack of muscle  pump, vasodilation in lower body, and lack of BP)  ○ Heat stroke → failure of hypothalamic temperature regulation → decreased sweat  rate → massive heat storage   ■ Mortality rate greater than 20% → heart failure and cerebral edema  ■ High core temperature (>41 C), hot dry skin, central nervous system  dysfunction  ■ Either hyper- OR hypotension  ■ Damage to sweat glands   ■ At risk include obese, unt, dehydrated, unacclimatized  ■ Immediately cool with water, fanning, and ice packs (on neck, groin, armpit -  major arteries)  ○     ● Hyponatremia  ○ Exercise-associated hyponatremia (EAH) = serum of plasma Na < 135 mmol/L  ■ Results in symptoms of altered function of CNS → weakness, dizziness,  lethargy (lack of energy of enthusiasm), vomiting, headache, seizure  ■ Can result from:  ● Signicant uid consumption and retention → dilution of plasma Na   + ● Signicant dehydration → large amount of unreplaced Na loss + ○ Predisposing factors for EAH among marathon runners are:  ■ Substantial weight gain  ■ Race time over 4 hours  ■ Female  ■ Low body mass index (underweight)  ○ EAH likely less common among competitive athletes  ■ Recreational endurance athletes should be cautious of over-hydration  ● Preventing Heat Injuries  ○ Allow for acclimatization → 2-4 weeks  ○ Do not rely on sensation of thirst → people normally only replace 33-66% of sweat  loss  ○ Rely on clinical symptoms of hyperthermia more than temperature measurements   ■ Hypo- or hypertension  ■ Profuse sweating or dry & hot skin  ○ Recognize conditions that predispose one to hyperthermia, including  ■ Fever   ■ Lack of adequate sleep  ■ Glycogen depletion  ■ Hypoglycemia  ■ Heavy alcohol consumption (diuretic → dehydrate)  ○ Record body weight every day before practice  ■ ↓ 2-3% → consume extra uid  ■ ↓ 4-6% → consume extra uid + reduce intensity  ■ ↓ >7% → consult physician  ● Proper Hydration  ○ Can gauge hydration status by several means:  ■ Changes in body weight → in the morning after peeing  ■ Color of urine → precaution when taking vitamin B supplements  ■ Urine osmolality → 100-300 mOsmol/kg normal, >900 dehydrated  ○ Goal to replace sweat loss with uid intake during exercise is dicult because:  ■ It is uncomfortable to drink that much uid when sweat rate is high  ■ High variability of sweat rates between individuals   ■ Thirst no a good indicator of uid need   ■ Rules of sports  ○ Pre-exercise hydration  ■ General recommendation → consume 6 ml H2O/kg BW every 2-3 hrs in the  days prior to exercise in heat  ● Weight uctuates only tiny bit (<1%) in a well-fed & hydrated state  ■ Consume ~16-24 uid ounces 2 hrs before practice or event, and 12 uid  ounces 15 min before  ■ Hyperhydration → lower HR and core temperature during exercise in the  heat  ● Problem with uid retention → improvement with glycerol  co-ingestion  ● Some evidence for improvement in performance  ○ During exercise hydration  ■ Consume ~8-12 uid ounces every 15 min during practice or event lasting  longer than 1 hr  ● 6-8% CHO solution  ● Small amount of electrolytes (500-700mg/L of Na )   + + ■ Increase Na intake to 1.5g/L if you routinely experience cramping  ■ Inclusion of electrolytes help to:  ● Increase palatability and maintain thirst  ● Prevent hyponatremia  ● Increase water absorption (SGLT-1 works better when both CHO & Na   + & H2O present)  ● Increase uid retention   ○   ○   ○ Rehydration after exercise is optimized by the inclusion of sodium and CHO →  promote active water absorption  ■ Plain water consumption → reduction in plasma sodium and osmolarity →  reduced thirst and increased urine output → delay in rehydration  ■ ^Na + uid = ^Rehydration  ○ Should try to ingest 150% of weight loss after exercise (1.5 L for every kg of weight  loss)  ■ Conventional 1 L/kg weight loss did not account for obligatory urine loss after  drinking  ■      


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