Fig. 2. Spring mechanics (vertical, craniocaudal and lateral) in Monodelphis domestica typical of all steps analyzed over a fivefold increase in speed (0.3-1.8 m s^-1). (A) Ground reaction forces, velocities of the center of mass, and vertical displacement of the center of mass. BW is body weight (0.833 N). Negative values in the craniocaudal record reflect braking effort whereas positive values are propulsive. The broken line indicates mean velocity. (B) Three-dimensional kinetic energies (KE), gravitational potential energy (PE), and total mechanical energy (ME) of the center of mass. Data are for a single diagonal couplet step from a 85 g individual moving at 1.046 m s^-1 with a duty factor of 43.75, limb phase of 52.08, % recovery of 1.36%, and total KE—PE phase shift of 8.18°. The diagonal couplet step began when the first limb of the couplet touched the ground and ended when the last limb of the couplet was lifted off.

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