Week 8 - Thermoregulation and thermal stress Flashcards
What is our normal resting body core temperature?
36.5-37.5 degrees Celsius
- Fluctuation throughout the day
In the heat, core temperature can safely increase up to .. degrees Celsius?
40 degrees Celsius
In the cold, core temperature can safely drop to .. degrees Celsius?
35 degrees Celsius
Define core temperature.
defined as temperature of the hypothalamus, the thermoregulator centre of the body.
How can core temperature be assessed?
- Oesophageal temperature
- Rectal temperature
- Stomach temperature (swallowed telemetry pill)
- Oral temperature
- Tympanic temperature
a) Skin temperature
b) Cool mean skin temp
c) warm mean skin temp
d) hot mean skin temp
32-35 degrees Celsius
<30
30-34.9
>35
What does the homeostatic maintenance of body temperature require?
the operation of temperature sensors (peripheral and central thermoreceptors) and regulated effectors (adrenal medulla, sweat glands, skin arterioles, skeletal muscles).
Describe physiological control of thermoregulation when body temperature INCREASES.
Blood vessels dilates
Sweat glands secrete fluid
–> heat is loss
Describe physiological control of thermoregulation when body temperature DECREASES.
Blood vessels constrict
Sweat glands do not secrete fluid
—> Heat is conserved
Shivering generates heat
–> heat is generated
Physiological mechanisms of heat loss
Blood reaching the skin (vasodilation)
Sweating
Physiological mechanisms of heat conservation/production
Shivering thermogenesis
Voluntary muscular activity
Non-shivering thermogenesis
Heat exchange between the body and environment governed by biophysical properties. What are biophysical properties dictated by?
the surrounding temperature, humidity and air motion, sky and ground radiation + clothing
What is the most challenging environment for exercise? Why?
Hot and humid - we cannot evaporate sweat from our skin.
We gain/lose heat chiefly through our…
shell/skin
Is skin temperature regulated?
NO - unlike core temperature it’s not regulated and it varies across the body in response to thermal environment.
What is our most powerful means of regulating body temperature?
behavioural responses
Why does core temperature increase when performing aerobic exercise in a hot environment?
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.
How does dehydration (loss of body water) influence exercise performance in the heat?
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.
Why is prolonged high-intensity exercise impaired by a hot environment?
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.
What is the most rapid way to lower body temperature?
cold water immersion
Identify methods that mitigate the impact of heat stress:
a) Before exercise
b) Immediately before exercise
c) During exercise
a) Heat acclimation and aerobic training
b) Pre-cooling, hydration status
c) Hydration, clothing, cooling
Identify acclimatization responses
- 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)
Hypothermia
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
How does cold water influence exercise performance (swimming)?
Due to shivering, oxygen consumption is higher in cold
water during sub-maximal exercise but reduced during maximal exercise.
Describe the physiological adaptations of cold acclimatization.
- 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.
Identify physiological responses to exercise in the cold.
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
How is endurance exercise impaired in hot and humid environments?
1) Accelerated muscle fatigue
2) Central NS dysfunction
3) CV dysfunction
During exercise, what % of energy produced is released as heat?
70-80%
What does an increase in body core temperature typically result in?
cutaneous vasodilation and sweating
