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Fig. 1. A hypothetical diagram of quadrupedal walking. The fore quarters and hind
quarters are represented as independent inverted pendulums. If the mass
distribution is equal between the fore and hind quarters and the limbs cycle
at evenly spaced time intervals, the pendular movements of the fore quarters
and hind quarters offset each other. When the fore quarters are highest (i.e.
gravitational potential energy is maximum), the hind quarters are lowest.
Similarly, when the fore quarters are moving fastest (i.e. maximum kinetic
energy), the hind quarters are moving slowest. As a result, the gravitational
potential energy (Ep) and kinetic energy
(Ek) are constant throughout the stride. Bars indicate
footground contact times, and the footfall order is left hind (LH),
left fore (LF), right hind (RH) and right fore (RF) limb. COM, center of
mass.