Inverse Dynamics of Jaculus jaculus jumps

Inverse dynamics of Jaculus jaculus jumps

Rivera, AM*; Moore, TY; Biewener, A

SICB 2014 Austin TX

17.1 (Cancelled due to polar vortex)

Jerboas (Jaculus jaculus) are small (~50g) bipedal rodents capable of jumping >0.5m in the air when startled. We used inverse dynamics to investigate the dynamics of these jumps (N=3; 20 jumps) in order to calculate the percentage of jump PE provided by elastic recoil of the tendons relative to muscle work. Force plate recordings of vertical and horizontal ground reaction forces were synched with high-speed video (250 fps) kinematics of the jump. Total tendon elastic energy storage never exceeded 17% of jump potential energy. This limited tendon elastic energy recovery by jerboas is similar to that observed during hopping in the morphologically convergent heteromyid kangaroo rat, Dipodomys spectabilis. To test the hypothesis that J. jaculus’ digital plantar hair tuft assists in locomotion on loose granular substrates, recordings were also made when jerboas jumped from a 1.5 cm layer of sand overlying the force plate before and after their digital hair tuft was shaved. No differences in jump height were observed for either condition of sand substrate jumps in comparison with earlier solid force plate trials. We conclude that these small bipedal rodents use their muscles to accelerate rapidly for energetically costly and sporadic locomotion, while larger hopping animals, like kangaroos, use their tendons to store and return elastic energy for energetically economical and sustained locomotion.

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