The Effect of Body Pitching on Leg-Spring Behavior in Quadruped Running

In this paper we investigated how the running speed would affect the dynamics of body pitching, and whether body inertia is important for animals. Passive trotting of spring-mass model and passive bounding of spring-beam model were studied at different speeds for different sets of body parameters respectively. Furthermore, different body inertias were used in bounding. We found that running speed exerts effect on leg performance by means of centrifugal force. The centrifugal force can be understood as an enhancement to the natural frequency of the spring-mass system. The disadvantage of body pitching may be offset by the great increase in centrifugal force at high speed. The results also reveal that body mass distribution might not be the main reason for the difference in maximal running speeds of different animals.