The role of fore‐ and hindlimbs during jumping in the Dybowski's frog (Rana dybowskii)

Abstract

Anurans are well known for their jumping abilities, making use of their strong hindlimbs. In contrast, the function of the forelimbs during take-off has rarely been studied. We measured the ground reaction forces exerted by forelimbs and hindlimbs during short jumps in the Dybowski's frog Rana dybowskii. Take-off occurred in two phases. Phase one (from the initial time until the forelimbs took off), which lasts a relatively long time (63.2 ± 4.1% of the total take-off phase, N = 20), provides sufficient time for the forelimbs to elevate the body to a suitable posture to deliver the best take-off angle. Phase two (from the forelimbs lift-off until hindlimbs lift-off) was dominated by the hindlimbs which provided a constant and fast elevation. The force angle (angle of the resultant vector from fore-aft and normal force components towards the plane of the substrate) of the hindlimbs and body trajectory was variable before the forelimbs lifted off of the substrate and then primarily followed the direction of the line from the foot-substrate point to the center of mass (COM). The preparation angle adopted when the forelimbs lifted off of the substrate was a good predictor of the take-off angle. The total normal force oscillated around body weight (BW) before the forelimb normal force peaked. The BW shifted from the hindlimbs to the forelimbs during the initial phase of take-off. A simple lever model suggests that the forelimbs are responsible for raising the COM, thus influencing the take-off angle in short jumps.

Inverse dynamic modelling of jumping in the red-legged running frogKassina maculata

“…Peak vertical force both exceeded and occurred earlier than peak horizontal force in K. maculata, similar to ranids Nauwelaerts and Aerts, 2006;Astley and Roberts, 2014;Wang et al, 2014) but unlike hylids . Maximum take-off velocities in K. maculata were slightly below average velocity reported in other frogs, whereas jump distance (scaled to SVL) was within the range reported for ranids but substantially lower than distances recorded in hylids ( Table 4).…”

“…Maximum take-off velocities in K. maculata were slightly below average velocity reported in other frogs, whereas jump distance (scaled to SVL) was within the range reported for ranids but substantially lower than distances recorded in hylids ( Table 4). The proximal to distal pattern of joint opening observed during jumping in K. maculata has been widely reported among frogs Peters et al, 1996;Nauwelaerts and Aerts, 2003;Astley and Roberts, 2014;Wang et al, 2014) and is thought to maximize foot-to-ground contact time, prolong acceleration (so that maximum velocity is reached as late as possible) and aid in elastic energy pre-storage (Bobbert and van Ingen Schenau, 1988;van Ingen Schenau, 1989;Wang et al, 2014). Range of movement and maximum values of extension for the ankle, knee, hip and sacroiliac joints in K. maculata are similar to those reported in other species Peters et al, 1996;Nauwelaerts and Aerts, 2003;Astley and Roberts, 2014).…”

Kinematic control of extreme jump angles in the red leg running frog (Kassina maculata)

“…After the onset of body motion, jumps proceeded in two phases: a slow 'preparatory' phase followed by a fast 'launch' phase. Similar to ranid frogs, the preparatory phase (roughly first ∼60-80% of duration) is marked both by forelimb contact (Wang et al, 2014) and slow acceleration of the COM (Fig. 4).…”

“…The present study addressed how frog joint kinematics shift to enable flexibility of jump angles. Because prior work found that forelimb preparation angle predicts take-off angle (Wang et al, 2014), we hypothesized an analogous 'joint preparation angle' whereby leg joints form a '3D extension plane' whose inclination is preset to determine final take-off angle (ψ take-off ; Fig. 1).…”

“…1). Given that frogs push their body upwards to reach a 'preparation angle' during the first phase of jumps (Wang et al, 2014), we similarly expect the limb joint axes to reach a 'joint preparation angle' enabling frogs to aim for a steep versus shallow jump. Specifically, we expect the rotation axes of the hip, knee and ankle to be approximately parallel such that leg segments move within the same plane (i.e.…”