Ciné films were used to study swimming in the frog, Hymenochirus boettgeri (Tornier) during near-vertical breathing excursions. The animals generally decelerated during hindlimb flexion (recovery phase) and accelerated throughout hindlimb extension (power phase). Body velocity patterns of frogs are distinct from those of other drag-based paddlers, such as angelfish and water boatman, where the body is accelerated and decelerated within the power stroke phase. The propulsive force, estimated for a single sequence from quasi-steady drag and inertial considerations, was positive throughout extension. The upper and lower bounds of this estimate were calculated by considering additional components of the force balance, including the net effect of gravity and buoyancy, and the longitudinal added mass forces associated with the body. Consideration of the force balance implies that simple drag-based propulsion may not be sufficient to explain the swimming patterns observed in frogs.

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