Graphics Reference
In-Depth Information
Quadruped Walks
We can study the details of a typical quadruped walk, but even taking into
account the movement of the individual legs, the sequencing of the leg
movements, the rotation at the shoulders and hips, the spine movement, and
the subtle actions of the head and tail, the study will still be a very general
one. There are many variations for individual species. However, this initial
investigation will still provide us with a reasonable starting point. Later in the
text and in the images we'll see other examples that could provide a useful
comparison.
At this point it might be worthwhile to briefly revisit the classifications
of action we've covered elsewhere, to help us analyze the action. As we
discussed in Chapter 3, we can break down most movements into three
quite distinct classifications: primary actions, secondary actions, and tertiary
actions. Having an understanding of how these classifications apply to any
given movement may provide a better understanding of that movement.
• Primary action: Cause
•
Secondary action: Supplement
•
Tertiary action: Effect
Primary actions
are those that provide the main source of any given
movement and without which the movement would not be possible. The
movement of the legs in a walk cycle is one such action.
Secondary actions
are those that assist in a movement and make a
contribution to the movement, though they are not necessary for the
movement to take place. Swinging arms in a walk may help with the walk but
are not vital to it.
Tertiary actions
describe those movements that occur as a result of other
movements and are affected by primary and secondary actions. Consider
the action of the tail of a horse as it runs. The tail's wave action is a result
of the run; it does not contribute to it. A tertiary action makes little or no
contribution to locomotion.
There are many aspects to even the most basic of walks. We must first
consider the part of an action that creates locomotion.
Duty factor
is a term
used to describe the part of a given action that contributes to the effort within
that movement. When applied to a walking action, the term describes the
period during which the individual feet are placed on the ground, providing
support and the power for forward locomotion.
When an animal wants to increase its speed during a walk, it naturally
lengthens the stride of each leg. It also increases the frequency of the step,
thereby reducing the duration of the duty factor of each step. Stride length
is determined by a number of factors, varies among animals, and varies by
motivating factors within individual animals. There are physical constraints
on the stride length, the main one being the actual length of the animal's leg
and the manner in which the legs are held (cursorial or nonecursorial). The
