Physiological Response to Exercise in the Cold PDF

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Exam 3 notes; Ondrak...

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Exercise and Environment I.

Physiological Response to Exercise in the Cold a. Shivering i. Uncontrolled skeletal muscle contractions b. Non-shivering thermogenesis i. Stimulates metabolism by SNS ii. Increasing metabolic rate increases internal heat production c. Peripheral vasoconstriction i. Occurs as result of SNS stimulation to smooth muscles surrounding arteriole in skin 1. Contraction (constriction) 2. Reduction in blow flow to outer “shell” areas

II.

Exercise in Cold a. Immersion in cold water increases heat loss through convection i. Exercise generates metabolic heat to offset some of loss b. Muscles weaken and fatigue more quickly when cool c. Exercise triggers release of catecholamines, which inc. mobilization for FFA as fuel i. In vasoconstriction, circulation is impaired to fat tissues and limits this d. Reduced dexterity in extremities due to reduced blood flow and slow nerve transmission e. Enhanced heat loss f. May result in hypothermia i. Loss of judgement g. Subcutaneous fat improves cold tolerance h. Decreased respiratory rate and volume i. Risk of frostbite (epithelial necrosis)

III.

Health Risks During Exercise in the Cold a. Hypothalamus loses ability to regulate body temperature below 94.1 degrees b. SA node is primarily affected by hypothermia i. HR drops, reducing CO

Exercise and Environment IV.

V.

VI.

Cold Acclimatization a. Shivering starts at lower skin temperature i. Increases in non-shivering thermogenesis help maintain heat b. Maintain higher hand and foot temperature i. Improved peripheral blood flow c. Improved ability to sleep in cold i. Due to reduced shivering d. Adaptations begin in one week Hypobaric (High Altitude) Environment a. Altitude i. Atmospheric pressure decreases with increasing altitude ii. PP gases 1. Same percentages, lower partial pressures b. CV responses i. Plasma volume initially decreases upon exposure to high altitude, but is eventually restored 1. Continued exposure results in increase RBC production ii. Adaptations result in greater total blood volume 1. Allows person to compensate for lower PO2 iii. Submax exercise during first few hours at altitude: 1. Increased HR 2. Decreased SV – reduced plasma volume c. Respiratory responses i. Pulmonary ventilation increases at higher altitudes 1. Rest and exercise 2. VE increases to bring in larger volume of air a. Ventilate more air because air is less dense ii. Hb saturation is 92% at 8,000 f 1. Decrease in PO2 iii. Decrease in a-VO2 difference 1. Sea level—55mmHg 2. 8,000 f—20mmHg d. Metabolic Responses i. Anaerobic metabolism and LA production increases at altitude because O2 is limited 1. At max effort, LA accumulation is lower in blood and muscles Effect of Altitude on Performance a. Short duration—anaerobic i. Reduced O2 transport to muscle does not limit performance 1. May increase performance via lower air resistance b. Long duration—aerobic i. Lower PO2 results in poorer performance 1. Dependent on oxygen delivery to muscle ii. Decreased VO2 max at altitude 1. Lower oxygen extraction

Exercise and Environment c. Max Aerobic Power i. Moderate altitude (~4000) 1. Decrease VO2 max due to decrease arterial PO2 ii. Higher altitude (>5000m) 1. Decrease VO2 max due to decrease CO a. Decrease max HR at altitude d. Submax Aerobic Power i. Higher HR 1. Due to lower oxygen content of arterial blood ii. Higher ventilation 1. Due to reduction in PO2 VII.

Acclimatization to High Altitude a. Production of more RBC i. Higher Hb content 1. Counters desaturation caused by lower PO2 b. Greater oxygen saturation i. Increased blood flow to lungs 1. Increase in nitric oxide

VIII.

Training for Competition at Altitude a. Effect on VO2 varies among athletes i. Due to degree of Hb saturation ii. Some athletes cannot improve VO2 max by training at altitude 1. Cannot train as intensely at high altitude b. Live at high altitudes, train at low altitudes i. Live high 1. Increase RBC production via EPO 2. >22hr/day at 2000-2500m required 3. Intermittent hypobaric hypoxia a. 3hr/day, 5days/wk at 4000-5000m ii. Train low 1. Maintain high interval training velocity 2. Some experience Hb desaturation iii. Mechanism 1. Improve VO2 max via increased RBC production 2. Improve mitochondria function, increase buffering capacity c. Live at low altitudes, train at high altitudes i. Live low 1. Avoids negative effects of prolonged altitude exposure a. Too much time at altitude can result in increased HR, plasma volume ii. Train high 1. No real changes in VO2 max or Hb concentration a. Cannot physically increase VO2 max at high, because cannot work as hard...