The gaits of chelonians: walking techniques for very low speeds

The gaits of three species of chelonians have been studied by filming and by recording the forces the feet exert on the ground. Chelonians could keep their bodies in equilibrium if they walked so as to have at least three feet on the ground at all times, and if the feet moved in appropriate sequence. However, they generally use a gait in which there are at times only two feet on the ground, and they do not maintain equilibrium, but pitch and roll through angular ranges of around 10°. Maintenance of equilibrium would require the feet to exert abruptly changing forces, which they are probably not capable of doing because of the slowness of chelonian muscle. Records of the forces exerted by the feet do not show abrupt changes. It is shown by mathematical modelling that if only slow changes of force are possible, the gaits and force patterns which chelonians use are close to the optimum which minimizes pitching and rolling. Gaits only a little different would be impracticable at low speeds because of excessive pitching and/or rolling. Slow muscle may be more efficient than fast muscle, and can maintain tension more economically.