Abstract
Desert Kangaroo rats (D. deserti) use erratic vertical leaps – over ten times their hip height, to evade snakes. These high-performance behaviors are fascinating as they seem to challenge muscle power limits at take-off, and the swing of their tails is suggested to help them to not only stabilize, but also maneuver in the air. This dissertation focusses on muscle-tendon dynamics during the jumping phase and on the role of the tail in maneuvering in the aerial phase of escape jumps in kangaroo rats.
Within animal models, muscle power often presents a limit to mechanical performance. Kangaroo rats, bipedal hopping rodents, use vertical leaps to outjump predators. Our research has shown that even submaximal jumps require as much as 340 W/kg muscle power, which suggests that maximal jumps – over 10 times their hip height – require more power than can be provided by muscle alone. We discovered that kangaroo rats achieve this high power output using their ankle extensor tendon (Achilles tendon) in two distinct ways simultaneously: to transfer energy from thigh and back muscles and to store elastic energy while decoupling the muscle fascicle shortening velocities in calf muscles from ankle flexion, allowing these muscles to operate under near optimal conditions for power production.
During their vertical escape jumps, kangaroo rats rotate their relatively long tail, as well as their body, through the air. Previous behavioral research on tail use in these rodents suggested that the tail is mainly used for balance. Video recordings show large tail swings in combination with a change in body orientation. In our studies, we found that the amount of degrees turned in the yaw plane is independent of jump height, jump distance, and aerial time. In addition, kangaroo rats re-orient in a ‘step-wise’ was, in which slower turning periods with tail segments center of masses being closely vertically aligned with the rotation axis of the body. Also, we showed that tails play an important role in re-orientation as tail and body angular momentum mirrored each other and had similar magnitudes.