Exercise Thermoregulation Flashcards
What is the challenge that is faced by the body during exercise?
Maintaining appropriate internal temperature during exercise
The muscles ability to function is not going to be as important as the body’s need to control core temperature, what does this mean?
This means that eventually we will need to redistribute the blood to the periphery to cool down the body - this takes blood away from working muscles so it will affect performance.
Humans can usually tolerate core temperature decline of ____ degrees and increase by ____ degrees; what does the difference imply about tolerance to temperature?
Decline in Tc by 10 degrees and increase by 5 degrees.
This implies that the body doesn’t tolerate heat as well as it tolerates cold.
What is the cutoff for core temperature (basically before you start to die)
> 40.5 degrees *(from ACSM article)
How is shivering used to keep us warm?
allows us to take advantage of the heat that is produced when our muscles are contracting
4 types of heat loss?
convection
conduction
evaporation
radiation
With regards to shivering, what happens if your core temperature drops too much?
You stop shivering - this means your core temp is so low that you cant even give energy to your muscles to contract, you must conserve all ATP to keep critical life functions happening. This is when we see frostbite and limb loss.
“heat transfer directly from one medium to another”
conduction
“transfer of heat through fluids”
convection
“transfer of heat in rays/waves/particles from a source - tends to be electromagnetic”
radiation
what is the best way to get rid of heat?
evapouration
in order for the body to lose heat, we have to have _____
evaporation
where is the coordinating center for temperature regulation and what is it called?
hypothalamus; preoptic-anterior hypothalamus
The preoptic anterior hypothalamus acts as a thermostat that is set and regulated at __ degrees (+/- 1 degree)
37
What are the two activating heat-regulating mechanisms?
- Thermal receptors in the skin –> input to central control center
- Changes in blood temperature perfusing hypothalamus directly stimulate central control centre
When responding to heat, what responses can the hypothalamus have?
cutaneous vasodilation and sweating
What are three factors that influence total amount of sweat vaporized from skin/pulmonary surfaces?
- Surface exposed to environment
- Temperature and relative humidity of ambient air
- Convection air currents about the body
What is the most important factor for determining effectiveness of evaporative heat loss?
relative humidity
“ratio of water in ambient air to total quantity of moisture that air could contain”
relative humidity
If you are sweating but it is not evaporating, what does this mean?
You are only losing fluids, and not heat. MUST evaporate to lose heat.
When do your sweating mechanisms start to slow down?
when you get up over 41 degrees - this is because you are wasting your valuable fluid - you will start to feel clammy because the blood flow to skin has stopped and now you have wet skin, giving a weird sensation
Will core temperature always increase at the beginning of exercise?
yes - doesnt matter if you are in a hot/humid environemetn or cool environment
What does the trend look like over exercise time for increase in core temperature in hot/humid environment?
never really levels off, this is because you have no way of getting rid of the heat you are producing.
During exercise as metabolic energy production begins, what is the first method for heat loss that kicks in?
convective heat loss begins immediately, however, is still only operating at a low level
There is a delay in evaporative heat loss post exercise, what does this contribute to?
More evidence for what drives EPOC - second slow part of epoc, we are producing heat as we are trying to get rid of it
There is an increase in body temperature with an increase in work rate; this relationship is _____
ALWAYS linear (for both arm and leg exercise) - temperature is proportional to active muscle mass
____ exercise intensity determines change in core temperature
relative
Is tympanic temperature a good measure of core temperature?
Nahh.. rectal would be better, and even better than rectal would be core temp. pill.
Body temperature during arm and leg exercise?
legs have bigger muscles therefore produce more heat!
How does ambient temperature influence heat production?
It doesn’t! It might influence our temperature, but not heat production.
As ambient temperature increase, what three things happen?
- heat production remains constant
- lower convective and radiant heat loss
- higher evaporative heat loss
Does energy output change with increasing ambient temperature?
noooooooooo
With increased exercise intensity, heat production ______
increases
Sweat production and electrolyte loss:
- top 3
- others?
- Sodium (predominate)
- Potassium (limited)
- Magnesium (trace)
- calcium
- chloride
Differences that occur during high vs low flow sweating?
Faster the fluid flows through the tubules, the less time we have to reabsorb it, and the more electrolytes we lose to sweat.
What are the concentrations of Na, Cl, and K in the interstitial fluid?
High Na and CL
Low K
What happens to skin temperature when we exercise in a hot environment?
Skin temp doesn’t really change because we need to keep temp down so that a heat gradient exists between environment and skin so we can evaporate heat
What happens to skin temp in humid vs dry conditions?
When it is humid you lose the vapour gradient and therefore you lose your ability to evaporate sweat, causing an increase in skin temperature
Organize from hottest to coolest:
- blood
- skin
- tissue
- environment
tissue
blood
skin
environment
Exercise in hot/humid environments:
-inability to lose heat has what effects (2)? What can these effects cause (2)?
- higher core temperature and higher sweat rate
- hyperthermia and impaired performance
Fatigue generally coincides with core temperatures between __-__
38-40
When fatigue from temperature occurs, what does it impair?
impairs muscle activation from high brain temperature –> this decreases central drive to exercise (unless you are crazy motivated)
Impaired exercise performance with inefficient thermoregulation leads to ___ and ___ loss as well as ____ changes
fluid & electrolyte
metabolic
Moderate exercise > 1hr = __-__L sweat loss
0.5-1.0
During dehydration, what happens to plasma volume and stroke volume?
lower plasma volume
reduced stroke volume
During dehydration, what happens to skin blood flow for a given temperature?
you see a depressed skin blood flow for a given core temperature
During dehydration, what happens to heart rate?
increased near-compensatory HR (due to reduction in SV and trying to maintain CO)
During dehydration, what happens to the efficiency of the circulatory and thermoregulatory systems in exercise?
general deterioration
Acclimatized person: sweat-related body water loss reaches peak of __L/hr during intense physical activity in the heat. Up to how many L/day?
3 L/hr
up to 12 L/day
What can happen with sweat-gland fatigue?
interferes with core temperature regulation
When you are acclimatized, you have an enhanced potential for evaporative cooling, but only under what condition?
only with adequate fluid replacement
Fluid loss of __% body mass adversely affects exercise performance.
2%
Dehydration results in reduction of what three things? This makes thermoregulation progressively more difficult.
plasma volume
peripheral blood flow
sweating rate
If you are using urine to assess dehydration, what measure makes it more accurate?
using urine specific gravity
What three things can be used in conjunction to assess dehydration?
urine
thirst
weight
What four mechanisms contribute to dehydration-mediated physical performance degradation?
- Augmented hyperthermia
- Increased CV strain
- Altered metabolic and CNS functions
- Increased perception of effort (RPE)
5 factors that modify heat tolerance?
- Acclimatization
- Training Status
- Age
- Gender
- Body fat level
