Lecture 14 - Temperature and fluid balance during exercise Flashcards

1
Q

__% of oxygen consumption ends up as heat

A

80%

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2
Q

What are means by which we lose heat?

A

radiation, conduction, convection and evaporation of sweat (the primary mechanism)

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3
Q

convection is the ..

A

movement of air across the skin

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4
Q

the water vapour pressure in the atmosphere will influence…

A

the evaporation of sweat,

would much rather exercise in dry heat not humid

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5
Q

What determines the core temperature and what is the major determinant?

A

The balance of heat production and heat loss

major determinant is exercise intensity

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6
Q

we do regulate our body core temperature, but because our heat loss mechanisms lag, there is a ‘‘temperature deficit’’ which is determined by the …

A

how intense the exercise is

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7
Q

rectal temperature has been shown to be a bit higher experimentally, why?

A

heat from the legs skews the results

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8
Q

What can happen if the muscle temperature gets really high?

A

can start to break down membranes/proteins - damage the muscle

people can die from this

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9
Q

at 20 degrees what proportion of heat loss is from sweat?

A

about half

and increasingly more as the temperature is raised above 20 degrees

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10
Q

If you were exercising in water, relative to air, what would be the differences in the proportion of heat lost by conduction and convection?

A

it would be a greater proportion

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11
Q

Sweating is regulated by not just core temperature, also ___ temperature

A

skin temperature

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12
Q

What makes up sweat?

A

Na, Cl, K+, Mg2+

of decreasing proportions

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13
Q

Is sweat hypertonic or hypotonic?

A

hypotonic (the major substance you lose with sweat is water)

sweat is an ultrafiltrate of plasma,

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14
Q

If your sweating at a higher rate, you’re Na concentration will be…

A

a bit higher as there isn’t enough time to reabsorb it along the sweat duct

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15
Q

Trained indivuduals will be better able to maintain their plasma Na, why?

A

aldosterone not only acts on the kidney but also the sweat duct

after training, aldosterone is stimulated to absorb Na to a greater extent - this helps maintain a higher plasma volume

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16
Q

At higher temperature more CO and oxygen uptake is going to…

A

the skin

raises the question of whether you should warm up on a hot day - could warm up the muscle temp, but will also redistribute the CO

17
Q

If you pre-expose to heat, and send alot of blood to the skin, the skin circulation means you will lose a bit of blood volume, meaning..

A

CO goes down, VO2 max goes down

18
Q

heat stress impairs exercise capability due to…

A

cardiovascular limitations, not glycogen or other fuel substrates

19
Q

True or False

Hyperthermia limits exercise performance?

20
Q

What are the observations which show Exercise-heat stress and its relationship to ‘‘central fatigue’’

A

Increased rating of perceived exertion

Reduced voluntary activation of muscle

Reduced Cerebral blood flow, but increased VO2 (probably not a major factor)

Hyperprolactinaemia - hormone released from pituitary (prolactin), if you get an increase in this its thought to reflect changes in the brain that are associated with fatigue
- there are high levels of this in the blood during exercise

21
Q

True or False

There is reduced neuromuscular performance with hyperthermia

22
Q

If the brain is getting hot, why is there reduced meuromuscular performance?

A

With hyperthermia, the brain needs to shut down the muscle as it is the producer of the most heat

a good protective reflex

23
Q

What are some strategies to enhance exercise performance in the heat?

A

Heat acclimatisation - get used to it

Pre-cooling

Fluid ingestion (to a lesser extent)

24
Q

What are the Physiological and metabolic adaptations to heat acclimatisation?

A

Increased BV

reduced HR

lower core and skin temps

Increased sweat rate and earlier onset

more dilute sweat

reduced muscle glycogen use

plasma adrenaline is lower

25
Fluid ingestion does what?
blunts the rise in core temperature
26
prior dehydration does what to exercise performance?
decreases performance
27
what are the physiological effects of fluid replacement?
you blunt the CV drift because you prevent the loss of SV (CO)
28
What are the benefits of fluid ingestion?
Increased BV Decreased HR Increased SV and CO lower core temp lower plasma Na+ and osmolality reduced muscle glycogen use enhanced exercise performance
29
what is responsible for promoting fluid and salt retention?
Increases in plasma renin and aldosterone
30
Is there good evidence that IV fluid replacement is better than oral?
no - over the longer term if it's an immediate emergency