Limb joint kinematics during vertical climbing and level running in a specialist climber: Gekko gecko Linneus, 1758 (Lacertilia : Gekkonidae)

Previous studies revealed that, despite clear morphological adaptations for climbing, performance and gait characteristics are barely affected when the specialist climbing lizard Gekko gecko is forced to run on its non-preferred level substrate. The present study focuses on the detailed joint kinematics of front and hind limbs to investigate whether this lizard modulates its limb movements while running on its non-preferred substrate. The intra-limb (fore and hind limbs) kinematic patterns were determined at three different speeds in G. gecko when climbing and running horizontally. Additionally, three-dimensional angles were determined at lift-off and at touch-down for both the fore and hind limbs over a wide range of running and climbing speeds. Generally, the intra-limb movement patterns used during level running are similar to those used when climbing. Moreover, the joint angles at lift-off and touch-down also show a high similarity for climbing and level running. There are some differences in joint angles: during climbing the shoulder and the elbow tend to be more extended at lift-off and touch-down compared to level running, and when the hind foot touches the substrate both the hip and the knee show a greater extension on level surface whereas the ankle is more extended during climbing. These differences can be grouped into two categories: the differences in the hip, ankle and wrist are likely to be related to the observed change in the posture and gait between climbing and level running. The changes in the shoulder, the elbow and the knee angles when G. gecko runs over-ground are likely to be the result of differences in the biomechanical constraints encountered during climbing and level-running.