Running Running allow animals to move faster than walking Unlike walking, there is no exchange happens between potential and kinetic energy during ground contact. Mechanism of running is similar to bouncing ball/pogo-stick    Once balls bounce off the ground, the kinetic energy decease while potential energy increase http://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamics/State_Functions/Kinetic_Energy Skeletal muscle stores energy by active stretching (bending knees) due to inertial, gravitational, or other gravitational force at first stance  Then, the energy is released as a spring-like bouncing mechanism when the legs are stretched out. As speed is increased, higher hip flexing become necessary. Therefore, the center of gravity on the vertical plane is higher during running.   http://newswatch.nationalgeographic.com/2011/03/25/cheetah-ambassador/               http://isci.greenwich.wikispaces.net/Farnum+-+Energy+Transformations

<O>