Hindlimb joint mechanics of desert jerboas during low- and high-speed jumping on sand.

Jerboas (Dipus sagitta) are small bipedal desert rodents that evade predators through irregular jumping. This study investigates how the hindlimb joints of jerboas achieve jumping at specific speeds. We hypothesized that the power output patterns of hindlimb joints are synchronized across different jumping speeds. To test this hypothesis, inverse dynamics analysis was employed to quantify the mechanical output of jerboas' hindlimb joints at varying jumping speeds. The maximum jumping speed of jerboas in this study reached approximately 2.5 m/s. Normal force and forward force act synergistically to provide power for sagittal-plane jumping. During high-speed jumping, the peak moments of the hip, knee, ankle, and metatarsophalangeal (MTP) joints were 0.895, 0.292, 0.803, and 0.295 N·m, respectively, all exceeding those at low speeds. The temporal sequence of peak joint power exhibited a proximal-to-distal transmission pattern. The peak powers of the hip, knee, ankle, and MTP joints during high-speed jumping were 10.52, 5.02, 7.45, and 0.06 W, respectively, which were also higher than those at low speeds. Thus, the results of this study did not support our initial hypothesis. However, the locomotion mechanism that uses the MTP joint as the final energy release node effectively enhances jumping efficiency and explosiveness. This study reveals the complex processes of energy generation, transmission, and absorption in the hindlimbs of jerboas under different jumping speeds, providing a crucial basis for a deeper understanding of the energy metabolic efficiency and mechanical optimization mechanisms underlying their jumping locomotion.