Graphics Reference
In-Depth Information
Along with an animal's physical attributes, natural selection has also ensured
the most appropriate gait that reflects the demands placed on that animal.
Walking and running are probably the two modes of locomotion that we are
most familiar with as humans because we do them on a regular basis, but
there are many more modes of locomotion using legs. Horses not only walk
and run, they trot, canter, and gallop. Even more modes of locomotion than
that are open to legged animals. And it is not only animals that have legs
that possess the ability to use different gaits. Swimming, flying, hopping,
jumping, crawling, climbing, burrowing—all have their uses. The ways in
which different animals choose to do any one of these varies a great deal. All
creatures that swim don't choose to use the same gait, and the gaits they do
choose may vary due to circumstance.
We will be taking a closer look at some of these movements later on in the
chapter. A very useful starting point is the definition of a gait that is offered by
Alexander (1989):
A gait is a pattern of locomotion characteristic of a limited range of
speeds, described by quantities of which one or more change discontinu-
ously at transitions to other gaits.
A particular gait or adjustment of a gait may depend on a number of factors
such as requirements for speed, economy of energy, or stability. The transition
from one gait to another can be a gradual process taking place over an
extended period of time; however, the actual change made from one gait to
another is usually a rather sudden process. The transition from a walk to a run
is usually a response to the efficiency of motion based on the energy costs of
one mode of locomotion over another one. Once the top speed of walking
is reached, it becomes more effective for the gait to be altered and another
gait to be adopted. The metabolic rate increases with the workload and it
becomes more efficient to make changes in the gait or mode of locomotion in
order to become more efficient.
Let's take a brief look at two very different case studies to illustrate the way
gaits may change throughout an action. First we consider a human walking
along a reasonably flat beach into the sea.
A human walking along a flat surface such as a firm, sandy beach will look
like the regular walk most of us do on a daily basis. The figure will remain
upright throughout the walk, with the length of the stride being fairly wide
and the knees lifted just enough for the feet to be raised clear of the flat
ground. This gait will be maintained even as the person steps into the very
shallow water on the shoreline. Then, as the figure continues to walk and
the water becomes deeper, the water will splash around the ankles and
shins, though the gait will remain the same. As the walk continues and the
water gets deeper still to around halfway up the shin, the walk will begin
to change. First the knees will be lifted higher so that the feet leave the
water. The figure at this point is stepping in and out of the water. A similar
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