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Lecture 4 – Exercise in the Heat
Exercise in the heat:
More chance of hyperthermia (high core temperature)
Hypohydration (dehydration from excess sweat)
Redistribution of blood flow (to the skin rather than supplying working muscles
Substrate availability (due to blood flow)
Body Temperature Regulation
Body temperature is maintained within a narrow range: 36.1 - 37.8
Humans are homeothermic (thermoregulation that maintains a stable internal body
temperature regardless of external influence)
In extreme cases, body temperature will deviate from the normal range (36.1-37.8°C).
E.g. heavy exercise, fever from illness and extreme hot or cold conditions.
Heat Balance
Metabolic Heat
Radiation/conduction and
Doing work produces heat convection
and some of this will
transfer to useful energy: The body will also radiate heat,
about 25% (meaning 75% loose heat through conduction
of energy produced is lost and convection
as heat) Loss = gain heat balance
Evaporation
Environmental Heat Loss > gain heat loss
The main heat loss mechanism:
Radiation, e.g. the sun. Loss evaporation
< gain heat
Sweat will gain
reduce
Conduction is when heat is heat.
transferred from one object
to the other. Convection is Thermoregulatory Control
when heat is transferred
from gasses or liquids, e.g. Internal body temperature is closely regulated by the
the air preoptic-anterior hypothalamus (located in the brain)
Thermoreceptors detect changes in temperature the sympathetic nervous system acts
in two main ways:
Vasodilation of blood vessels at the skin
Sweat glands become active, increasing evaporative heat loss.
Thermoreceptors detect heat loss and there is reduced activity of the sympathetic ns
(negative feedback loop)
Physiological Responses to Exercise in the Heat
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