Week 8 - Thermoregulation and thermal stress

Question 1

What is our normal resting body core temperature?

Answer 1

36.5-37.5 degrees Celsius
- Fluctuation throughout the day

Question 2

In the heat, core temperature can safely increase up to .. degrees Celsius?

Answer 2

40 degrees Celsius

Question 3

In the cold, core temperature can safely drop to .. degrees Celsius?

Answer 3

35 degrees Celsius

Question 4

Define core temperature.

Answer 4

defined as temperature of the hypothalamus, the thermoregulator centre of the body.

Question 5

How can core temperature be assessed?

Answer 5

• Oesophageal temperature
• Rectal temperature
• Stomach temperature (swallowed telemetry pill)
• Oral temperature
• Tympanic temperature

Question 6

a) Skin temperature
b) Cool mean skin temp
c) warm mean skin temp
d) hot mean skin temp

Answer 6

32-35 degrees Celsius
<30
30-34.9
>35

Question 7

What does the homeostatic maintenance of body temperature require?

Answer 7

the operation of temperature sensors (peripheral and central thermoreceptors) and regulated effectors (adrenal medulla, sweat glands, skin arterioles, skeletal muscles).

Question 8

Describe physiological control of thermoregulation when body temperature INCREASES.

Answer 8

Blood vessels dilates
Sweat glands secrete fluid
–> heat is loss

Question 9

Describe physiological control of thermoregulation when body temperature DECREASES.

Answer 9

Blood vessels constrict
Sweat glands do not secrete fluid
—> Heat is conserved

Shivering generates heat
–> heat is generated

Question 10

Physiological mechanisms of heat loss

Answer 10

Blood reaching the skin (vasodilation)
Sweating

Question 11

Physiological mechanisms of heat conservation/production

Answer 11

Shivering thermogenesis
Voluntary muscular activity
Non-shivering thermogenesis

Question 12

Heat exchange between the body and environment governed by biophysical properties. What are biophysical properties dictated by?

Answer 12

the surrounding temperature, humidity and air motion, sky and ground radiation + clothing

Question 13

What is the most challenging environment for exercise? Why?

Answer 13

Hot and humid - we cannot evaporate sweat from our skin.

Question 14

We gain/lose heat chiefly through our…

Answer 14

shell/skin

Question 15

Is skin temperature regulated?

Answer 15

NO - unlike core temperature it’s not regulated and it varies across the body in response to thermal environment.

Question 16

What is our most powerful means of regulating body temperature?

Answer 16

behavioural responses

Question 17

Why does core temperature increase when performing aerobic exercise in a hot environment?

Answer 17

Increase demand on heat loss mechanisms (increase skin blood flow and sweating).

But in hot environments, we get a reduced gradient between core and skin. Therefore, core temp increases as we can’t offload the heat as well as usual.

Question 18

How does dehydration (loss of body water) influence exercise performance in the heat?

Answer 18

Exacerbates heat stress impacts.

It decreases sweat rate (needs to keep body water circulating in the blood) and decreases plasma volume.
Further ↓ cardiac output, maximal oxygen uptake, muscle strength and work capacity.

Question 19

Why is prolonged high-intensity exercise impaired by a hot environment?

Answer 19

Competing regulatory demands for blood flow between thermoregulation, working muscles and CNS.

Heart-related changes (Incr. HR, reduced SV due to redistribution of blood) in skeletal muscle function and metabolism.

Question 20

What is the most rapid way to lower body temperature?

Answer 20

cold water immersion

Question 21

Identify methods that mitigate the impact of heat stress:
a) Before exercise
b) Immediately before exercise
c) During exercise

Answer 21

a) Heat acclimation and aerobic training
b) Pre-cooling, hydration status
c) Hydration, clothing, cooling

Question 22

Identify acclimatization responses

Answer 22

• Improved cutaneous blood flow (to the skin)
• Lower threshold for start of sweating (evaporative cooling begins earlier)
• Lower skin and core temperatures and heart rate for standard exercise (frees greater CO to active muscle)
• Effective distribution of cardiac output (skin and muscle)
• Increased sweat output (maximizes evaporative cooling)

Question 23

Hypothermia

Answer 23

core temperature below 35 degrees Celsius
* 2°C drop associated with maximal shivering
* 4°C drop associated with ataxia and apathy
* 6°C drop associated with unconsciousness
* Further drop associated with ventricular fibrillation, reduced brain blood flow,
asystole, death

Question 24

How does cold water influence exercise performance (swimming)?

Answer 24

Due to shivering, oxygen consumption is higher in cold
water during sub-maximal exercise but reduced during maximal exercise.

Question 25

Describe the physiological adaptations of cold acclimatization.

Answer 25

• Increased non-shivering thermogenesis: results in lower skin temperature at which shivering begins.
• Improved peripheral blood flow: ability to prevent large decreases in skin temperature (hand and foot temp) during cold exposure improved.
• Improved ability to sleep in the cold: due to reduced shivering.

Question 26

Identify physiological responses to exercise in the cold.

Answer 26

1) Reduced skin blood flow: peripheral vasoconstriction

2) Increased submaximal V02: greater heat loss

3) Increased ventilation during submaximal exercise: increase sympathetic stimulation

4) Increased lactate concentration: increases carb metabolism

5) Lower lipid mobilization: reduced blood flow to adipocytes

Question 27

How is endurance exercise impaired in hot and humid environments?

Answer 27

1) Accelerated muscle fatigue
2) Central NS dysfunction
3) CV dysfunction

Question 28

During exercise, what % of energy produced is released as heat?

Answer 28

70-80%

Question 29

What does an increase in body core temperature typically result in?

Answer 29

cutaneous vasodilation and sweating