EXPH 387: Chapter 25; Exercise and Thermal Stress
Muscular activity: exercise maintains a constant core temperature in areas as cold as ______?
-30 C
The sweat loss for moderate-intensity exercise lasting more than one hour is between ____ and ____ L
.5 and 1.0 L
a CLO unit of ___ maintains a sedentary person at ____ Met indefinitely in an environment of ___ C and ____ % humidity
1,1 Met, 21 C, 50%
at 38-40C
1. Higher brain temps decrease central drive to exercise 2. impaired muscle activation/depressed neuromuscular drive 3. depressed GI blood flow and increased permeability of toxins
What is evaporation from skin and pulmonary surfaces influenced by?
1. SA exposed to the environment 2. temp and relative humidity of the ambient air 3. convective air currents about the body
How is exercising in the heat resulting in increased lactate accumulation
1. decrease uptake at the liver because of vasoconstriction 2. reduced muscle catabolism because increase in diverting to the periphery
Evaporation and sweating:
1. during heat loss: eccrine sweat glans secrete large quantities of sweat 2. evaporation of sweat from the skin creates a cooling effect 3. the cooled skin in turn cools the blood diverted from interior tissues to the surface
Exertional Heat Stress compared to cooler conditions
1. earlier accumulation of lactate 2. encroachment on glycogen reserves 3. premature fatigue during prolonged moderate exercise
what are the features of the peripheral thermal receptors?
1. early warning system 2. free nerve endings in the skin 3. responsive to rapid changes in heat and cold 4. cold receptors
there is a compensatory vasoconstriction in splanchnic and renal vascular beds:
1. exercise and blood flow increases 2. GI & Kidney blood flow decrease
what two ways is body temperature regulated:
1. keeps temp between 37 C +/- 1 C 2. can not turn off- only can protect the body from heat buildup or heat loss
during exercise in the heat, a competition exists between:
1. mechanisms that maintain a large muscle blood flow 2. thermoregulatory mechanisms
what are the features of the cold receptors of the peripheral thermal receptors?
1. more numerous 2. exist near the skin surface 3. initiate regulatory response to cold
two competing dements when one exercises in heat:
1. muscle requires blood to sustain energy metabolism 2. arterial blood (diverts to the periphery to transport metabolic heat for cooling at skin surface)
what are the four physical processes that facilitate heat loss:
1. radiation 2. conduction 3. convection 4. evaporation
Fluid deficits:
1. reduce the ability to dissipate heat 2. increase the rate of heat storage and CV strain
what are the early warning signs of Peripheral Thermal Receptors:
1. sends sensory information to the hypothalamus and cortex 2. evokes appropriate physiological adjustments
what are physiological mechanisms involved in
1. the transfer of heat to the periphery 2. the loss of heat from the body 3. the regulation of overall core body temperature
Maintenance of BP:
1. visceral vasoconstriction increases total vascular resistance 2. intest exercise with accompanying dehydration
in aquatic environments conduction...
1. water absorbs several thousand times more heat than air 2. water conducts heat away from the warmer body parts 3. lose more heat in water
Shivering during exercise:
1. will occur during strenuous activity if the core temp remains low 2. when shivering stops the metabolic rate of the individuals falls, shivering may not be able to prevent a decline in core temperature 3. muscle fatigue will not depress the shivering response
sweat rate can increase to ____ L/hour
2.0 L/hour
during exercise metabolism can increase ___ to ___ times above resting
20 to 25 x (1C ever 5 to 7 min)
with extreme heat ______ % of CO passes through the skin
25-30%
average cutaneous blood flow rate is about __________ mL/min in a thermoneutral environment
250 mL/min
acclimatized individuals can lose water at a rate of approximately ___ L per hour through sweating
3 L
shivering along increases whole body metabolism by __ to __ fold
3 to 5
how many kcal of heat are lost per liter of water vaporized?
580 kcals
higher heart rates at ____ submit levels of exercise in heat
ALL (this does not offset decreased SV)
temperature regulation is _______ in order to _____ BP and muscle blood
compromised, maintain
Radiation
consists of electromagnetic heat waves
Hypothalamus
contains specialized neurons that coordinate and control temperature regulation of the body
CO: Maximal Exercise
decreased SV, proportional to fluid deficit and reduced blood volume
overall Cardiac Output...
decreases
as SV ____, HR _____
decreases, increases
Conduction
direct heat transfer required molecular contact (through solid, liquid, or gas)
what is the best defense against overheating?
evaporative cooling
shivering
exercise metabolism; can produce an oxygen consumption of approx. 1200 mL/min
what increased the risk of heat illness
exercising in a dehydrated state
T/F Trained and Untrained athletes have different core temps at any given %Vo2
false they are the same
aldosterone
from kidney, increase in Na reabsorption (increase in fluid, by decrease in urine output)
Posterior hypothalamus responsible for
heat conservation
anterior hypothalamus responsible for
heat loss
Evaporation:
heat loss via water vaporizing from the respiratory passages and skin surface
how does conduction work
heat moves through deep tissues to the cooler skin surface
what does increased metabolic rate increase?
heat production
sweat remains ______ to other body fluids
hypotonic
when will core temperature rise
if the heat gain exceeds heat loss (seen during prolonged and intensive exercise)
hypovolemia from sweating _____ plasma osmolality
increases
CLO unit
index of thermal resistance
what does the CLO unit indicate
insulating capacity of any layer of air trapped between skin and clothing
shivering
involuntary muscle contractions
how is extra heat production in trained individuals lost?
larger sweat output
Football uniforms
limit heat exchange
what creates a zone of insulation?
little air movement or convection, this minimizes further conductive heat loss
Core temp during exercise: aerobically fit individuals perform _____ & _______ higher levels of hyperthermia
longer, tolerate
convection
loss of heat due to movement of air or water adjacent to the skin
As sweating increases, both water (plasma) and electrolytes are _______
lost --- blood becomes hypertonic
Ideal clothing in the heat:
most clothing is more effective in allowing evaporative heat loss (cottons and linens absorb moisture)
does radiation require molecular contact
no
loss of body water impairs exercise events that take longer than ____ minute
one minute
what does thermoregulations primarily protect against?
overheating
effects of clothing on thermoregulation
reduces radiant heat in warm environments and helps prevent conductive and convective heat loss in the cold
what is the most important factor when determining how well evaporative cooling functions?
relative humidity
sweating starts within several _______ of the start of vigorous exercise (evaporation)
seconds
Ideal clothing in the cold:
several layers of light clothing lined with various materials often provide the best benefits 1. blocks air movement 2. allows water vapor from sweating to escape 3. saturation of a garment affects heat exchange
Cardiac Output: Submaximal Exercise
similar CO in hot and cold
what does the decrease in plasma and electrolytes cause?
specific hormones are released
Thermoregulation in cold stress: vascular adjustments
stimulation of the cutaneous cold receptors (vascular adjustments, muscular activity, and normal output)
what is conduction influenced by
temperature gradient and thermal qualities of the surface
Heat transfer: temperature gradient can flow from:
the body to the environment in extreme cold, increase heat production and minimize heat loss to prevent a decline in core temp
what happens to the effectiveness of conduction, convection, radiation, and evaporation when ambient air exceeds body temperature
the effectiveness is reduced
what was the CLO unit developed by?
the military
how is excessive body fat beneficial in cold environments
the receptors are on the medial part of the body, excess body weight would create a larger barrier with the periphery
what initiates coordinated response?
the temperature of the blood heightens activity and stimulated the hypothalamus
Thermal Balance
the temperature of the body's inner tissues is dependent on the factors that add/subtract body heat
why what the CLO unit developed?
to develop standards for the insulate properties of clothing and to meet environmental challenges
T/F: almost any level of dehydration can compromise performance and the ability to maintain thermal balance
true
vasopressin (ADH)
water moves back to blood (from hypothalamus)
does a fit individual generate more total heat?
yes
what can the average cutaneous blood flow rate fall to in environments that are extremely cold
zero
what is the main physiological system maintaining thermal balance?
circulatory system
Cardiac Output
CO = SV x HR
what are compromised in hot environments?
CV function and exercise capacity
increased heat production occurs because of what two "calorigenic" adrenal medulla hormones?
Epinephrine, Norepinephrine
Thermodynamics: Max Ex: L O2- Min -1, and Max EX kcal-min-1
Max Ex: O2: 4 L, 20 Kcal
Thermodynamics: Resting O2-Min -1, and resting kcal-min-1
Resting O2: 0.25 L, Kcal: 1.3
prolonged cold exposure results in the increased release of what hormone?
Thyroxine
T/F: physiological means that regulate heat loss are the same regardless of internal or external means
True
sweat is what type of solution
a hypotonic saline solution
what does the hypothalamus act as
a thermostat
what forms the basis of the wind chill temperature index?
air flowing over the body produces a cooling effect
what accelerates heat loss?
air passing ex. riding a bike
hormonal adjustments are stimulated by:
aldosterone and vasopressin (ADH)
Other hormones that play rolls in the increased heat production?
aldosterone and vasopressin (antidiuretic)
Exertional Heat Stress: greater dependence on ____ metabolism compared to cooler conditions
anaerobic
what are changes in blood temperature detected by?
anterior hypothalamus
at what temperature does physiological symptoms become impaired?
between 38 and 40 C
in radiation the ________ is usually warmer than the _____
body, environment
relative workload determines what
change in core temperature with exercise 50% Vo2 max = 37.3 C 775% Vo2 max = 38.5 C