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The
Human Powerplant
Human energy expenditure in various types of motion is illustrated
in the diagram. It is seen that the bicycle represents a significant
advantage in terms of energy use as compared to walking, running or skating
at the same speed. In all cases the, energy requirement increases super-linearly
with the increase in velocity. The curve showing the power required to
overcome drag due to the air suggests that very little work is lost to the mechanical
components of the bicycle. At 7 m/s, 86% of the energy expended by
a cyclist is used to overcome the air resistance. For a skater at the same
speed, the same air resistance accounts for only about 57% of the total energy
used, the increase in total energy usage indicating the lower efficiency of
this mode of travel.
Under steady state conditions, the energy use should
correspond to energy production by the body, and this depends upon the rate
of oxygen consumption by the body. This is known as the aerobic mode. |
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