Biomechanics of Frog Swimming: II. Mechanics of the Limb-Beat Cycle in Hymenochirus Boettgeri

The hindlimb kinematics of Hymenochirus boettgeri (Tornier) were investigated using high-speed ciné films. The movement pattern was stereotypic, flexion and extension of the metatarsal-phalangeals and feet always lagging behind flexion and extension of the femora and tibiofibulae. The right hindlimb was modelled as a series of linked circular cylinders and a flat plate. A blade-element approach was used to calculate the quasi-steady drag-based and accelerative force components parallel to the direction of motion, based on the hindlimb kinematics of sequence 1 (see preceding paper). Positive thrust is generated primarily during the initial stages of extension (power stroke) because of unsteady (added mass) effects. Negative thrust occurs over the latter half of extension, despite the continued acceleration of the animal. Hindlimb interaction is thought to provide propulsive thrust for the latter half of the extension phase. It is suggested that a jet and/or reflective effect may be involved.