Body Heat in Exercise
Almost all the energy released by the body’s metabolism of
nutrients is eventually converted into body heat. This applies even to the
energy that causes muscle con-traction for the following reasons: First, the
maximal efficiency for conversion of nutrient energy into muscle work, even under
the best of conditions, is only 20 to 25 per cent; the remainder of the
nutrient energy is con-verted into heat during the course of the intracellular
chemical reactions. Second, almost all the energy that does go into creating
muscle work still becomes body heat because all but a small portion of this
energy is used for (1) overcoming viscous resistance to the move-ment of the
muscles and joints, (2) overcoming the friction of the blood flowing through
the blood vessels, and (3) other, similar effects—all of which convert the
muscle contractile energy into heat.
Now, recognizing that the oxygen consumption by the body can
increase as much as 20-fold in the well-trained athlete and that the amount of
heat liberated in the body is almost exactly proportional to the oxygen
con-sumption, one quickly real-izes that tremendous amounts of heat are
injected into the internal body tissues when performing endurance athletic
events. Next, with a vast rate of heat flow into the body, on a very hot and
humid day so that the sweat-ing mechanism cannot eliminate the heat, an
intolera-ble and even lethal condition called heatstroke can easily develop in the athlete.
Heatstroke. During endurance athletics, even undernormal
environmental conditions, the body tempera-ture often rises from its normal
level of 98.6° to 102° or 103°F (37° to 40°C). With very hot and humid
condi-tions or excess clothing, the body temperature can easily rise to 106° to
108°F (41° to 42°C). At this level, the ele-vated temperature itself becomes
destructive to tissue cells, especially the brain cells. When this happens,
mul-tiple symptoms begin to appear, including extreme weakness, exhaustion,
headache, dizziness, nausea, profuse sweating, confusion, staggering gait,
collapse, and unconsciousness.
This whole complex is called heatstroke,
and failure to treat it immediately can lead to death. In fact, even though the
person has stopped exercising, the tempera-ture does not easily decrease by
itself. One of the reasons for this is that at these high temperatures, the
temperature-regulating mechanism itself often fails. A second reason is that in
heatstroke, the very high body temperature itself approximately doubles the
rates of all intracellular chemical reactions, thus liberating still more heat.
The treatment of heatstroke is to reduce the body temperature as
rapidly as possible. The most practical way to do this is to remove all
clothing, maintain a spray of cool water on all surfaces of the body or
continually sponge the body, and blow air over the body with a fan. Experiments
have shown that this treatment can reduce the temperature either as rapidly or
almost as rapidly as any other procedure, although some physicians prefer total
immersion of the body in water containing a mush of crushed ice if available.
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