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ch 15 - Flashcards

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Class:PHED 35345 - Exercise Physiology (with lab)
Subject:Physical Education
University:Rowan University
Term:Fall 2014
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Thermoregulation
Normal body temperature fluctuates several degrees during the day in response to physical activity, emotions, and ambient temperature variations.
Body temperature exhibits diurnal fluctuations:
  • Lowest temperatures occur during sleep.
  • Slightly higher temperatures persist awake.

Contributing factors to heat gain and loss to regulate core temperature at 98.6°F (37°C).
Thermal Balance Equation
+M-E+/-TR+/-CD+/CV+SR
Where:
M = Metabolism
E = Evaporation
TR = Thermal Radiation
CD = Conduction
CV = Convection
SR = Solar Radiation

Core Temperature During Physical Activity
  • Heat generated by active muscles increase core temp to fever levels that incapacitate a person if caused by external heat stress alone.
Increased core temp with PA does not reflect heat dissipation failure.
  • Modest core temperature increase reflects favorable internal adjustments that create optimal thermal conditions for physiologic and metabolic function
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Intense PA for 2 to 3 hrs can induce dehydration
Can impede heat dissipation and compromise CV function and performance

Average water loss per hour from sweating at various air temp during rest and light and moderate PA

Fluid Loss in Physical Activity
  • For acclimatized person, sweat loss peaks at 3 L·h−1 during intense PA in heat and averages nearly 12 L/d.
  • Intense sweating for several hr induces sweat gland fatigue that impairs core temp regulation.
  • Hot, humid environ impede effectiveness  of evaporative cooling and promotes large fluid losses

Consequences of Dehydration
Any dehydration impairs physiologic function and thermoregulation.
Plasma volume decreases as dehydration progresses:
  • Peripheral blood flow and sweating rate decrease to make thermoregulation more difficult.
  • Premature fatigue occurs from reduced plasma volume that increases HR, RPE, core temp.
Loss of plasma volume produces two effects:
  1. Initiates increases in systemic vascular resistance
  2. Reduces skin blood flow

Factors That Affect Sweat-Loss Dehydration
PA intensity
PA duration
Environmental temp
Solar load
Wind speed
Relative humidity
Clothing
Water Requirements (L·H−1) for rest and varying intensities of PA in the heat; indoors and outdoors at diverse temperatures and RH.

Generated by Koofers.com
Water Replacement and Rehydration
  • Adequate fluid replacement sustains evaporative cooling of acclimatized humans.
  • Proper scheduling of fluid replacement maintains plasma volume for optimal circulation and sweating progress.
  • Well-hydrated athletes always function at a higher physiologic and performance level than dehydrated athletes.

Acclimatization Repeated heat exposure with PA improves capacity for PA with less discomfort; optimal acclimatization requires adequate hydration.
Exercise training
Training increases sweating response sensitivity and capacity so sweating begins at a lower core temperature.

Thermoregulatory adjustments over 9-day heat acclimatization period
Generated by Koofers.com
PA for 2- to 4-hr exposure daily produces almost complete acclimatization after 10 days.
Age-related vascular changes include
depressed peripheral sensitivity that impairs cutaneous vasodilation from two factors:
  1. Modified sensitivity of thermoreceptors
  2. Limited sweat gland output
  3. Dehydration-limited sweat output with insufficient fluid replacement

Aging delays sweating onset and blunts magnitude of sweating response due to :
Smaller release of vasomotor tone
Less active vasodilation when sweating begins

Existing Age-Related Thermoregulatory Differences: Children
Prepubescent children show lower sweating rate and higher core temperature during heat stress.
Children take longer to heat acclimatize.
Children exposed to environmental heat stress should exercise at a reduced intensity and receive additional time to acclimatize.

Generated by Koofers.com
Gender and Thermoregulation
  • Women and men equally tolerate physiologic and thermal stress of PA when matched for fitness and acclimatization levels.
  • Gender differences occur for four thermoregulatory mechanisms:
  1. Sweating
  2. Evaporative versus circulatory cooling
  3. Body surface area-to-mass ratio
  4. Menstruation

Excess body fat
  • Excess body fat negatively impacts performance in hot environments.
  • Fat’s specific heat exceeds that of muscle tissue to insulate the body’s shell to retard peripheral heat conduction.
  • Large overfat persons possess a smaller body surface area-to-mass ratio for sweat evaporation compared with leaner, smaller persons.
Excess body fat directly adds to energy expended in weight-bearing activities.

Cold Weather Physical Activity
Human exposure to extreme cold produces considerable physiologic and psychologic challenges.
Cold ranks high among the differing terrestrial environmental stressors for its potentially lethal consequences.Body loses heat 2 to 4 faster in cool water compared with air at the same temperature.
  • Metabolic heat generated by muscular activity contributes to thermoregulation during cold stress.
  • Individual differences in body fat content significantly effects physiologic function in a cold environment during rest and PA.

Five factors compromise core temperature regulation in the cold
  1. Chronic exertional fatigue
  2. Sleep loss
  3. Inadequate nourishment
  4. Reduced tissue insulation
  5. Depressed shivering heat production

Generated by Koofers.com
Acclimatization to Cold
Humans adapt more poorly to chronic cold exposure than heat exposure.
  • Increased heat production does not accompany body heat loss; individuals regulate at a lower core temperature in the cold.
  • Repeated cold exposure of hands or feet brings about blood flow increases through these anatomic regions during cold stress.

Early warning signs of cold injury include:
  • Tingling and numbness in fingers and toes
  • Burning sensation in nose and ears
  • Disregarding signs of overexposure leads to frostbite
Generated by Koofers.com

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 Thermoregulation
Normal body temperature fluctuates several degrees during the day in response to physical activity, emotions, and ambient temperature variations.
Body temperature exhibits diurnal fluctuations:
  • Lowest temperatures occur during sleep.
  • Slightly higher temperatures persist awake.

 Contributing factors to heat gain and loss to regulate core temperature at98.6°F (37°C).
 Thermal Balance Equation
+M-E+/-TR+/-CD+/CV+SR
Where:
M = Metabolism
E = Evaporation
TR = Thermal Radiation
CD = Conduction
CV = Convection
SR = Solar Radiation

 Core Temperature During Physical Activity
  • Heat generated by active muscles increase core temp to fever levels that incapacitate a person if caused by external heat stress alone.
Increased core temp with PA does not reflect heat dissipation failure.
  • Modest core temperature increase reflects favorable internal adjustments that create optimal thermal conditions for physiologic and metabolic function
 Intense PA for 2 to 3 hrs can induce dehydration
Can impede heat dissipation and compromise CV function and performance

Average water loss per hour from sweating at various air temp during rest and light and moderate PA

 Fluid Loss in Physical Activity
  • For acclimatized person, sweat loss peaks at 3 L·h−1 during intense PA in heat and averages nearly 12 L/d.
  • Intense sweating for several hr induces sweat gland fatigue that impairs core temp regulation.
  • Hot, humid environ impede effectiveness  of evaporative cooling and promotes large fluid losses

 Consequences of Dehydration
Any dehydration impairs physiologic function and thermoregulation.
Plasma volume decreases as dehydration progresses:
  • Peripheral blood flow and sweating rate decrease to make thermoregulation more difficult.
  • Premature fatigue occurs from reduced plasma volume that increases HR, RPE, core temp.
Loss of plasma volume produces two effects:
  1. Initiates increases in systemic vascular resistance
  2. Reduces skin blood flow

 Factors That Affect Sweat-Loss Dehydration
PA intensity
PA duration
Environmental temp
Solar load
Wind speed
Relative humidity
Clothing
Water Requirements (L·H−1) for rest and varying intensities of PA in the heat; indoors and outdoors at diverse temperatures and RH.

 Water Replacement and Rehydration
  • Adequate fluid replacement sustains evaporative cooling of acclimatized humans.
  • Proper scheduling of fluid replacement maintains plasma volume for optimal circulation and sweating progress.
  • Well-hydrated athletes always function at a higher physiologic and performance level than dehydrated athletes.

 AcclimatizationRepeated heat exposure with PA improves capacity for PA with less discomfort; optimal acclimatization requires adequate hydration.
 Exercise training
Training increases sweating response sensitivity and capacity so sweating begins at a lower core temperature.

 Thermoregulatory adjustments over9-day heat acclimatization period
 PA for 2- to 4-hr exposure daily producesalmost complete acclimatization after 10 days.
 Age-related vascular changes include
depressed peripheral sensitivity that impairs cutaneous vasodilation from two factors:
  1. Modified sensitivity of thermoreceptors
  2. Limited sweat gland output
  3. Dehydration-limited sweat output with insufficient fluid replacement

 Aging delays sweating onset and blunts magnitude of sweating response due to :
Smaller release of vasomotor tone
Less active vasodilation when sweating begins

 Existing Age-Related Thermoregulatory Differences: Children
Prepubescent children show lower sweating rate and higher core temperature during heat stress.
Children take longer to heat acclimatize.
Children exposed to environmental heat stress should exercise at a reduced intensity and receive additional time to acclimatize.

 Gender and Thermoregulation
  • Women and men equally tolerate physiologic and thermal stress of PA when matched for fitness and acclimatization levels.
  • Gender differences occur for four thermoregulatory mechanisms:
  1. Sweating
  2. Evaporative versus circulatory cooling
  3. Body surface area-to-mass ratio
  4. Menstruation

 Excess body fat
  • Excess body fat negatively impacts performance in hot environments.
  • Fat’s specific heat exceeds that of muscle tissue to insulate the body’s shell to retard peripheral heat conduction.
  • Large overfat persons possess a smaller body surface area-to-mass ratio for sweat evaporation compared with leaner, smaller persons.
Excess body fat directly adds to energy expended in weight-bearing activities.

 Cold Weather Physical Activity
Human exposure to extreme cold produces considerable physiologic and psychologic challenges.
Cold ranks high among the differing terrestrial environmental stressors for its potentially lethal consequences.Body loses heat 2 to 4 faster in cool water compared with air at the same temperature.
  • Metabolic heat generated by muscular activity contributes to thermoregulation during cold stress.
  • Individual differences in body fat content significantly effects physiologic function in a cold environment during rest and PA.

 Five factors compromise core temperature regulation in the cold
  1. Chronic exertional fatigue
  2. Sleep loss
  3. Inadequate nourishment
  4. Reduced tissue insulation
  5. Depressed shivering heat production

 Acclimatization to Cold
Humans adapt more poorly to chronic cold exposure than heat exposure.
  • Increased heat production does not accompany body heat loss; individuals regulate at a lower core temperature in the cold.
  • Repeated cold exposure of hands or feet brings about blood flow increases through these anatomic regions during cold stress.

 Early warning signs of cold injury include:
  • Tingling and numbness in fingers and toes
  • Burning sensation in nose and ears
  • Disregarding signs of overexposure leads to frostbite
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