The adhesive mechanisms of climbing animals have become an important research topic because of their biomimetic implications. We examined the climbing abilities of hylid tree frogs on vertical cylinders of differing diameter and surface roughness to investigate the relative roles of adduction forces (gripping) and adhesion. Tree frogs adhere using their toe pads and subarticular tubercles, the adhesive joint being fluid-filled. Our hypothesis was that on an effectively flat surface (adduction forces on the largest 120 mm diameter cylinder were insufficient to allow climbing), adhesion would effectively be the only means by which tree frogs could climb, but on the 44 and 13 mm diameter cylinders, frogs could additionally utilise adduction forces by gripping the cylinder either with their limbs outstretched or by grasping around the cylinder with their digits, respectively. The frogs' performance would also depend on whether the surfaces were smooth (easy to adhere to) or rough (relatively non-adhesive). Our findings showed that climbing performance was highest on the narrowest smooth cylinder. Frogs climbed faster, frequently using a 'walking trot' gait rather than the 'lateral sequence walk' used on other cylinders. Using an optical technique to visualise substrate contact during climbing on smooth surfaces, we also observed an increasing engagement of the subarticular tubercles on the narrower cylinders. Finally, on the rough substrate, frogs were unable to climb the largest diameter cylinder, but were able to climb the narrowest one slowly. These results support our hypotheses and have relevance for the design of climbing robots.

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Animals can adjust movement pattern to balance the outside disturbance to keep stability. In this paper a rat Rattus norregicus was focused to study its balancing strategy to lateral impact. A pendulum was used to strike lateral thorax and lateral abdomen of the animal. Locomotion behavior was recorded by a high speed camera and ground reaction forces were measured by 3-dimensional forces sensors array synchronously during the whole progress of impact and adjustment. The result showed that the balancing strategy to lateral impact in a rat was closely related to the striked position of the body. The rat bent flexible body to absorb the impact energy when encountering the lateral thorax strike, and it resisted the impact force and torque through its side-sway and left leg supporting when encountering the lateral abdomen strike. Animal spent less time on side-sway than on body bending during imergency buffer, but it spent more time on side-sway than on body bending when reverting to original locomotion gait. Balancing strategy to lateral impact in a rat can be inspired to improve the robustness of bionic robot.