Kinematics of gecko climbing: the lateral undulation pattern.

Geckos are exceptional at terrestrial locomotion and can move on diverse terrains and surface orientations. Geckos employ cyclical lateral bending of their flexible trunk and tail to coordinate their limb movements. In this study, using an optical motion capture system, we measured the kinematics of this lateral undulation pattern of geckos (Gekko gecko) at increasing locomotion velocity on horizontal plane, 45 degrees inclined plane and vertical plane, respectively. We observed that geckos increased their stride frequency and stride length to increase the locomotion velocity; the effect of stride frequency on the locomotion velocity was greater than that of stride length. With increasing speed, the lateral undulation pattern changed from standing to travelling. The waveform of the trunk movement appeared as single-peak curves in a standing wave at low speeds and was propagated from head to tail in a travelling wave at high speeds. Analysis of the anatomical characteristics and axial angular kinematics of the two patterns revealed that the lateral undulation pattern results from girdle rotation and axial muscle activity. Thus, the travelling wave is the combined effect of the lateral trunk bending and deflection of the body relative to the motion direction.