Lecture 33: Thermal Stress

Question 1

What is the normal range of body temperature?

Answer 1

36.5 –> 37.5

Question 2

What are the consequences of excessive heat stress?

Answer 2

Heat stroke and brain damage

Question 3

What area of the body is core temperature taken from and why?

Answer 3

The hypothalamus because it is the temperature control centre of the body
There are also no heat changes in this part of the body

Question 4

Give a brief description of the four ways in which body temperature can be measured.

Answer 4

Oral (affected by hot drinks and exercise)
Rectal (affected by blood temperature of exercising lower limbs)
Tympanic (measures brain blood temperature but can be affected by heat loss due to sweating)
Stomach (most effective and can move through GI tract to get an overall picture of body temperature)

Question 5

What is the average skin temperature?

Answer 5

32.5 –> 35

Question 6

What is the determinant of an object’s temperature?

Answer 6

Its kinetic energy

Question 7

How do we equate heat storage?

Answer 7

S = M +/- Cv +/- Cd +/- R - E

Question 8

What are our heat loss mechanisms?

Answer 8

Conductance
Convection
Radiation
Evaporation

Question 9

What are our heat gain mechanisms?

Answer 9

Metabolism (BMR)
Convection 
Conductance 
Radiation 
Postural changes 
Thermic effect of food 
Muscle activity 
Hormones 
Environment

Question 10

Why does our metabolic heat production rise with exercise intensity?

Answer 10

Because we perform more aerobic/anaerobic energy conversion which produces ATP and 75% heat

Question 11

What is the key reason we cannot store heat?

Answer 11

Denaturation of key enzymes

Question 12

Describe conductance.

Answer 12

Travel of heat down a temperature gradient when two objects are in direct contact with one another
3% of heat loss
How heat is passed between cells
Dependent on: a) conductivity of an object b) temperature gradient

Question 13

Describe convection.

Answer 13

Travel of heat between an object and moving fluid or air
12% of heat loss
Depends on: a) temperature gradient b) velocity of moving substance c) conductance of object d) surface area of substance

Question 14

As described by the wind-chill index, what is the effect of increased wind speed on internal temperature?

Answer 14

Increased wind-speed lowers internal temperature (increased velocity of flow)

Question 15

Describe radiation.

Answer 15

Heat loss/gain due to EM waves
60 % of heat loss
Depends on: a) temperature gradient b) area of exposed surface c) colour d) reflectivity

Question 16

What is latent heat of evaporation?

Answer 16

The quantity of heat lost via sweat evaporation

Question 17

Describe evaporation.

Answer 17

The loss of heat via sweating
25% of heat loss
Depends on: a) temperature gradient b) surface area exposed c) convection currents d) humidity of the room

Question 18

Which areas of the body does the hypothalamus stimulate to control temperature?

Answer 18

Sympathetic stimulation to: adrenal medulla (epinephrine)/ sweat glands/ skin arterioles
Involuntary motor response: skeletal muscles

Question 19

What is the effect of body temperature on cardiac functions and blood volume during VO2 max?

Answer 19

Increased body temperature increases heart rate and lowers blood volume and therefore stroke volume

Question 20

Describe the integrated CV response to exercise and how it is affected by increased heat.

Answer 20

Increased blood flow to cutaneous system due to requirement to lose heat
This lowers the central blood volume as blood volume is lost as sweat
This lowers venous return to the right ventricle and therefore amount of blood that can be oxygenated by lungs
This causes vasoconstriction of non-exercising regions and increased heart rate

Question 21

Why do we have greater vasodilation to the skin at rest?

Answer 21

Because there is less competition between the skeletal muscle and the cutaneous system for blood flow

Question 22

What is the effect of dehydration on the body?

Answer 22

It decreases: plasma volume, cardiac output, sweat loss, work output by muscles, liver glycogen

It increases: heat storage and tolerance to heat stress

Question 23

Why does sweating increase despite its inability to cool the body in high humidity and the negative consequences it has on blood volume?

Answer 23

The body can regulate heat loss via the hypothalamus, but there is no regulatory system that has the means to regulate the amount of sweat loss, therefore as the body gets hotter the hypothalamus just continues to increase sweat output

Question 24

What are the physiological response to heat acclimatization?

Answer 24

Sweat loss: early stage of exercise; covers more body areas; more sweat loss

Decreased HR, increased cutaneous blood flow, more effective distribution of cardiac output

Question 25

Describe how heat illness can develop.

Answer 25

Heat syncope –> heat cramps –> heat exhaustion –> heat stroke

Question 26

What is the best treatment for decreasing body temperature?

Answer 26

Cold water immersion

Question 27

Describe the factors that affect heat injury.

Answer 27

Fitness (better acclimisation/ more sweat loss) 
Hydration 
Humidity 
Wind 
Clothing 
Environment (convection/radiation)
Metabolic Rate (exercise intensity)

Question 28

What temperature is the body during hypothermia and what are the stages decline due to hypothermia?

Answer 28

Below 35
Two degree drop: maximum shivering
Four degree drop: ataxia and apathy
6 degree drop: unconsciousness

Question 29

What has been found to be the effect of the cold on oxygen consumption during sub-maximal and maximal exercise?

Answer 29

Sub-maximal exercise in the cold leads to an increased VO2 due to shivering

Question 30

What are the physiological responses to decreased temperature?

Answer 30

Decreased lipid breakdown 
Decreased skin blood flow 
Decreased heart rate 
Increased central blood volume 
Increased submaximal VO2

Question 31

Describe cold acclimitisation.

Answer 31

Takes one week
Shivering threshold occurs earlier on
Improved peripheral blood flow
Improved ability to sleep