Dynamics of geckos running vertically.
Geckos with adhesive toe pads rapidly climb even smooth vertical surfaces. We challenged geckos (Hemidactylus garnotii) to climb up a smooth vertical track that contained a force platform. Geckos climbed vertically at up to 77 cm s(-1) with a stride frequency of 15 Hz using a trotting gait. During each step, whole body fore-aft, lateral and normal forces all decreased to zero when the animal attached or detached its toe pads. Peak fore-aft force was twice body weight at mid-step. Geckos climbed at a constant average velocity without generating decelerating forces on their center of mass in the direction of motion. Although mass-specific mechanical power to climb was ten times the value expected for level running, the total mechanical energy of climbing was only 5-11% greater than the potential energy change. Fore- and hindlegs both pulled toward the midline, possibly loading the attachment mechanisms. Attachment and detachment of feet occupied 13% and 37% of stance time, respectively. As climbing speed increased, the absolute time required to attach and detach did not decrease, suggesting that the period of fore-aft force production might be constrained. During ascent, the forelegs pulled toward, while hindlegs pushed away from the vertical surface, generating a net pitching moment toward the surface to counterbalance pitch-back away from the surface. Differential leg function appears essential for effective vertical as well as horizontal locomotion.
Autumn
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K
Department of Biology, Lewis & Clark College, Portland, OR 97219-7899, USA.
Hsieh
S T
ST
Dudek
D M
DM
Chen
J
J
Chitaphan
C
C
Full
R J
RJ
D000268:Adhesiveness; D000704:Analysis of Variance; D000818:Animals; D001696:Biomechanical Phenomena; D005552:Forelimb / Q000502:physiology*; D005684:Gait; D006614:Hindlimb / Q000502:physiology*; D008116:Lizards / Q000235:genetics*; D012420:Running / Q000502:physiology*; D013997:Time Factors