FURROW, E.*; AHN, A.N.; BIEWENER, A.A.; Harvard University, Cambridge, MA: Mechanics of a Running Frog (Kassina maculata)

Although most frog species are specialized for jumping, hopping or swimming, Kassina maculata, the Red-Legged Running frog, primarily uses locomotion during which the hind limbs alternate. In this study, the mechanics of the center of mass during locomotion were analyzed to determine whether Kassina frogs do indeed run, as their common name suggests. Mechanically, walking and running can be classified by the relationship between the horizontal kinetic energy (E_kh) and the gravitational potential energy (E_p) of the animal’s center of mass during a stride. To obtain values for E_kh and E_p, ground reaction forces were acquired as the frogs (n=13 animals; average mass = 8.38 � 1.55g, S.D.) locomoted across a miniature force plate with simultaneous high-speed, digital video data. In some trials (average speed = 0.133 � .025ms^-1), the fluctuations in the horizontal kinetic energy and gravitational potential energy of the center of mass were out of phase (phase shift = 118 � 21.4&deg) indicating an inverted pendulum or walking gait. In these walking trials, the animals were found to recover as much as 44.2% of the external mechanical energy during the stride. In faster trials (average speed = 0.187 � .039ms^-1), the fluctuations in the horizontal kinetic energy and gravitational potential energy of the center of mass were in phase (phase shift = 16.8 � 16.4&deg) indicating that the animals used a bouncing or running gait. The mechanics of the center of mass during locomotion in Kassina maculata demonstrate that these frogs walk at slower speeds and run at faster speeds, despite the lack of an aerial phase.