Graphics Reference
In-Depth Information
lower speeds generated by slow-twitch muscles are powered by aerobic
metabolism, which involves the release of energy by oxidizing food to carbon
dioxide and water. The rate at which the power is able to be released depends
on the speed with which the respiratory and circulatory systems can supply
the muscle fibers with oxygen.
In short, anaerobic metabolism powers short-sprint activities; aerobic
metabolism provides the power for sustained locomotion. Athletes who exert
maximum effort for 10 seconds derive around 85% of the energy to do so
from anaerobic metabolism. In 10 minutes of maximum effort, 10% to 15%
of energy is derived from anaerobic metabolism. In two hours of maximum
effort, around 1% of energy is gained in this manner.
Fast-twitch anaerobic and slow-twitch aerobic fibers generally appear
alongside one another in the limb muscles of mammals. However, in fish
these different muscle types are segregated, with the red slow-twitch aerobic
muscles running along the body on the outer surface and the white fast-
twitch anaerobic muscles on the inner.
For some animals it has not become important to move at anything other
than very slow speeds. This has resulted in the animals using their slow-twitch
muscles for much of the time. Slow muscles are much more economical in the
way they burn energy and they require less energy intake. This may be very
useful if the food supply is not very plentiful or if the animal lives on a very
poor diet consisting of material with a low calorie content. A giant tortoise
that is capable of eating large quantities of food when available is also able to
go for long periods without food or drink.
A cheetah is highly dependent on speed for its survival and has developed
thigh muscles that are 50% heavier than those of a typical quadruped of the
same body mass. Anaerobic metabolism plays a far more important role for
this animal than for the more sedentary tortoise.
Energy consumption is a vital part of an animal's existence. The more efficient
animals are at locomotion, the more energy they are able to conserve, and
in so doing they are able to turn energy from food into growth, fitness
maintenance, or reproduction.
Tendons
It was originally thought that the only purpose of tendons was to connect
muscle to bone. However, it is now realized that the elastic properties of
tendons enable them to behave like a spring, allowing them to both store
and release energy and thereby making a contribution to locomotion.
As tendons are stretched or compressed, they store energy, and then on
recoiling they release that stored energy and assist the related muscle in
generating locomotive power. Working in conjunction with the muscle, the
tendon enables the muscle to generate a greater force; in doing so it makes a
contribution to the conservation of energy.
