Graphics Reference
In-Depth Information
between these two phases, the supporting legs provide the highest levels
of thrust, creating forward locomotion. In the phases that follow, what was
undertaken by the front left leg is now undertaken by the front right leg until
the cycle is completed.
The Gallop
The transition from a standing repose position or a walking gait into a running
one may be abrupt. Galloping occurs when walking or trotting is no longer
the most effective and efficient gait. Rather like the trot, the galloping gait is
distinguished from a walking gait by the inclusion of a suspension phase, a
part of the action when all legs are suspended of the ground.
FIG 4.29 A much simplified
galloping action of a quadruped.
Unlike the walk cycle, galloping for a quadruped presents an asymmetrical
action of the legs, and as a result the sequence of leg movements changes
from a walk to a run. In addition to the suspension phase, there are two
distinct points in the gallop when the animal is supported on only a single
foot: as it lands from the suspension phase and again as it jumps.
By compressing and flexing its spine, the animal is able to increase the reach
of its legs and therefore increase its stride length. In a gallop it is normal for
hind legs to land in a position forward of the point where the hind legs left the
ground. This is most noticeable in the cheetah, where the extreme flexibility
of its spine allows its hind legs to reach well forward of the front ones.
The highly simplified illustration demonstrates how the hind legs and forelegs
cross and the spine compresses and arches. It also indicates that the rotation
of the body mass imparts a kind of forward and backward rocking action in
the animal. Throughout this action the head is held relatively still.
The five phases described in the following sections are intended to represent
a full gallop cycle in a little more detail, illustrating the sequence of all four
legs and the use of the individual joints and pivotal points.
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