(4A, Ch25) Thermal Stress Flashcards
Rise in core temperature during exercise is dependent on…
A. whether or not a person is wearing heavy uniform, pads, and helmet
B. whether or not it’s sunny
C. work intensity
D. whether or not it’s humid
E. all of the above
E. all of the above
What is the main cause of heat production?
Through muscle contraction
(NOTE: this is directly related to workout)
what are the 4 ways body heat can be lost?
- radiation
- conduction
- convection
- evaporation
During aerobic exercise under hot conditions, blood flow to the skin is ________ than under temperate conditions, so blood flow to skeletal muscle is _________ than under temperate conditions.
higher; lower
_____ is how a person perceives heat, taking into account humidity
heat sensation
On a day with low humidity, 85 degree Fahrenheit temperature, and bright sun, what is the primary means of heat exchange from the body to the environment during aerobic exercise (e.g. an hour run)?
A. heat lost in the breath
B. muscle contractions
C. evaporation of sweat
D. radiation
E. convection
C. evaporation of sweat
Main contributors to body heat (4)
- solar radiation (AKA sunlight)
- metabolic rate
- physical activity
- thermic effect of food
aerobic training _____ sweat NaCl concentration
decreases
Compared to exercise under temperate conditions, during exercise in hot conditions, blood flow to the skin is:
A. lower
B. higher
C. about the same
B. higher
What is a limiting factor in rehydration?
gastric emptying rate
Sodium in drink when rehydrating after exercise decreases urinary output. Why?
retains fluid AKA improving hydration
If core temp is constant, total heat loss is _____
the same
If core temps increases, ______ increases
sweating rate
Evaporative heat loss is more efficient in ____ temps
high temps
(increases w increasing temps)
Core temp and swimming
decreases, especially in winter when water temps are lower
Sodium in drink when rehydrating after exercise _____ urinary output
decreases
heat acclimation increases ____
performance
Dehydration impairs _____
aerobic performance
What is the effect of the following heat acclimatization response:
Inreased sweat output
Maximizes evaporative cooling
What does fluid replacement do in aerobic events under hot conditions?
improves performance
What happens to the core temperature at rest? At maximal exercise?
Rest: remains the same
Maximal exercise: increases
At low air temperatures (e.g. 40 degrees Fahrenheit), which is most important to body heat loss?
A. convection
B. evaporation
C. radiation
A. convection
(NOTE: not much sun–not much radiation; not hot out so not much evaporation)
Which is greater?
A. maximal rate of sweating
B. maximal rate of rehydration
C. they’re always the same
A. maximal rate of sweating
(NOTE: up to 2L can be lost)
Who has a higher heart rate during low workload conditions?
Elderly
What is the effect of the following heat acclimatization response:
Lower threshold to begin sweating
evaporative cooling begins earlier
At low temperatures, a portion of VO2 goes towards _____
shiverign
_____ is water produced by oxygen consumption by the electron transport chain.
Metabolic water
Under conditions of low humidity, evaporative heat loss is greater than dry heat loss at…
A. 10 degrees C
B. 37 degrees C
C. evaporative heat loss is never greater than dry heat loss
D. evaporative heat loss is always greater than dry heat loss
B. 37 degrees C
Fluid loss during exercise is between _____ L per hour
1-2
At what air temperature would resting energy expenditure be greatest for someone wearing shorts and a t-shirt?
0 degrees C
20 degrees C
40 degrees C
air temperature doesn’t affect VO2
0 degrees C
When does humidity impair evaporation?
When it is high
Which statement about water loss and fluid replacement is false?
A. The thirst mechanism always underestimates fluid loss during work in the heat and after work ends.
B. You should take frequent drinks throughout the work period.
C. If you drink 250 milliliters (about 1 cup) every 15 minutes, you can replace 1 liter per hour.
D. If, during prolonged periods of work in the heat, weight loss exceeds 2 percent, the person should rehydrate before returning to work or exercise.
E. Marathon runners are wise to drink as much as possible before the event and to drink as much as possible as frequently as possible during the event.
E. Marathon runners are wise to drink as much as possible before the event and to drink as much as possible as frequently as possible during the event.
Compared to exercise under temperate conditions, during exercise in hot conditions, maximal aerobic work rate is
A. higher
B. lower
C. about the same
B. lower
Trained subjects lose ____ salt in sweat than untrained
less
Clothing _____ core temperature and skin temperature
increases
Compared to exercise under temperate conditions, during exercise in hot conditions, blood flow to skeletal muscle is:
A. lower
B. higher
C. about the same
A. lower
Sweating rates are greater when it’s ____ and ______
why?
hot; humid
sweat doesn’t evaporate as rapidly, imparing ooling
DELETE Heat production amounts to evaporative heat loss
it is greater
Does dehydration have an effect on exercise other than aerobic exercise?
Does not affect strength or anaerobic performance
Relationship between evaporative and convective cooling
Inverse; as one increases, the other decreases
conduction vs convection
Conduction: heat transfer directly to solids (ex: muscle to skin contact)
Convection: heat transfer to air/liquid (ex: heat transported in blood)
Convective cooling is more efficient in _____ temps
low
(decreases w increasing temps)
A wet bulb globe temperature is a way of measuring….
heat stress using air temp to give an indication of heat conditions beyond air temp alone.
Increased blood flow to skin ______ aerobic performance
decreases
What does sweat rate depend on? (3)
- work rate
- air temp
- body size
As core temperature increases, _____ blood flow goes to the skin compared to muscles
more
Which is greater?
A. metabolic heat production capacity (assuming a VO2 of 4 liters/min, each liter of O2 is equivalent to 5 kcal)
B. capacity for evaporative cooling (assuming maximal sweat rate of 30 ml/min, complete evaporation of the sweat, and a heat loss of 0.6 ml/ml of sweat that’s evaporated)
C. they’re the same, that’s why core temperature never changes
A. metabolic heat production capacity (assuming a VO2 of 4 liters/min, each liter of O2 is equivalent to 5 kcal)
How long does it take to get the heat acclimatization benefits?
About 2 weeks
Aerobic training increases RBC count in the ____
later weeks
Convective cooling is least effective….
A. when air temperature is equal to or greater than skin temperature
B. when swimming in water cooler than body temperature
C. when it’s windy
D. when the air temperature is low (e.g. 40-50 degrees Fahrenheit)
A. when air temperature is equal to or greater than skin temperature
What types of events are impaired in the heat?
aerobic events
The ____ the aerobic workload, the ____ the core temperature
greater; greater
endurance, work capacity declines if you lose _____% of body weight through fluid loss
2
5 benefits of heat acclimatization
- INCREASED sweating
- DECREASED water loss
- DECREASED salt concentration in sweat
- INCREASED blood volume
- INCREASED blood distribution
Risk of hyperthermia ______ with heat and humidity
increases
Effect of wind on convective and evaporative cooling
increases both
Fluid replacement limits the rise in _____ and _____
core temp; and HR increases
As sodium content increases, there is ____ retention of fluids (optimal: 50 mmol Na)
greater
While resting, how much body heat is produced?
Very minimal; it increases during exercise
When temps are high, blood flow to the ___ increases to aid in cooling, thus decreasing blood flow to _____
skin; the muscle
Aerobic training increases plasma volume in the ____
first weeks
If the air temperature on this day were higher than skin temperature, such as on a summer day in Arizona, there _____ be convective cooling
wouldn’t
What is the gastric emptying rate?
250 mL every 15 mins
