HLTH2200 Lecture Notes - Lecture 2: Heat Exhaustion, Heat Cramps, Heat Stroke
15 Jun 2018
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Exercise in the heat
• How do we respond?
dehydration
Sweat, vasodilation
Breathing rate increases
Affects structure of enzymes (metabolic processes)
Loss of salts
• What are the problems?
Body temps rises
We lose minerals and electrolytes
• How does that affect performance?
• Dehydration?
• Core temperature?
• Ability to offload heat?
• What can we do about it?
Drink plenty of water
• Other considerations
Heat exhaustion
Heat stroke
Heat Stress
• Hot environment can severely impair exercise capacity
– Increased heat storage may result in hyperthermia, heat exhaustion and
heatstroke.
– Heat exhaustion may occur in prolonged intense activity in varying
environments
• Also recognised as a risk in occupational settings
– How does heat stress occur in cool conditions?
• Exercise tolerance is lower in 20oC than 10oC
Direct effects of hyperthermia
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Direct effects of hyperthermia
• Systemic insufficiency in the cardiovascular system (during exercise)
– Due to?
• Decreased work output/ voluntary termination of exercise
– Consistent results in
• Highly fit 39.3oC
• Moderately fit 38.7oC
• Catastrophic theory of fatigue or central governor?
• Maintain core temp
Complications from excessive heat stress
• Those more prone to heat stress are:
– the overweight
– the unacclimatized
– poorly conditioned individuals
– those who exercise in a dehydrated state
– those with a previous history of a heat illness episode (reduced tolerance)
• Immediate action is to reduce the heat stress and re-hydrate the person until
medical help arrives
– TC?
– [Na+]?
Warning Signs
Hyponatraemia low sodium concentrations!!
• Low plasma sodium concentration
• Signs and symptoms may include
1. Nausea and vomiting.
2. Headache.
3. Confusion.
4. Loss of energy and fatigue.
5. Restlessness and irritability.
6. Muscle weakness, spasms or cramps.
7. Seizures.
8. Coma.
• Thought to aout for a large uer of heat stroke ases i rereatioal athletes
ho trael slo ad drik a lot…
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How do we respond to Heat?
Lines of Defence against hyperthermia
• 1st line of defence
– Redirection of blood flow
– How? Where? Why?
• 2nd line of defence
– Increased sweat rate usually in TA range 28 – 30°C
• Sweat rate is also dependent on rate of heat production
– Increased Body Temp? Controversial!
Maintaining Thermal Balance in the heat
• Exercise results in heat production
– >70% of metabolic energy is converted to heat during mechanical movement
– Heat production
• At rest ~70-100W
• Mild Walking pace 280-350W
• Heavy Exercise >1000W
Stored heat
Stored heat = (Tc2 – Tc1) x 0.83 (kcal·kg-1·°C-1) x bwt (kg)
Time (hr) x BSA (m2)
• Can be positive or negative depending on the environmental conditions
• Need to factor in radiation, convection conduction
• SH = Metabolism – Work + (R + C + K) – Evap
• R+ C+ K may be positive or negative depending on the heat gradient
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Exercise in the heat: how do we respond? dehydration. Heat stress: hot environment can severely impair exercise capacity. Increased heat storage may result in hyperthermia, heat exhaustion and heatstroke. Heat exhaustion may occur in prolonged intense activity in varying environments: also recognised as a risk in occupational settings. How does heat stress occur in cool conditions: exercise tolerance is lower in 20oc than 10oc. Direct effects of hyperthermia: systemic insufficiency in the cardiovascular system (during exercise) Due to: decreased work output/ voluntary termination of exercise. Consistent results in: highly fit 39. 3oc, moderately fit 38. 7oc, catastrophic theory of fatigue or central governor, maintain core temp. Complications from excessive heat stress: those more prone to heat stress are: the overweight the unacclimatized. Poorly conditioned individuals those who exercise in a dehydrated state those with a previous history of a heat illness episode (reduced tolerance) Immediate action is to reduce the heat stress and re-hydrate the person until medical help arrives.
