Meeting Abstract
Desert kangaroo rats (D. deserti) are soft sand specialists that rely on sand dunes to construct their burrows. However, throughout the territories in which they forage, kangaroo rats can experience a wide range of substrates and obstacles, including hard and soft sand, rocks, and dense shrubs. The mechanical demands of hopping on these different surfaces can vary greatly. When hopping on soft sand, mechanical energy is lost to the substrate as the sand shifts under the animals’ feet. This energy must be replace by mechanical work generated by muscles. The goal of this study was to determine how the lateral gastrocnemius (LG), a large ankle extensor muscle, contributes to the additional work required for hopping on soft sand. We used sonomicrometry and tendon force buckles to quantify the mechanical output of the LG as kangaroo rats hopped on a custom-built rotary treadmill with hard and sandy surfaces. Preliminary results showed that there were no differences in gait timing between hard and sandy surfaces and the ankle extensors produced similar peak forces (hard: 9.96 +/- 0.77 N, sand: 9.45 +/- 1.13 N). However, due to a slight reduction in LG muscle strain, the net work developed by the LG tended to decrease when hopping on sand (0.93 +/- 0.25 mJ), relative to the hard surface (0.68 +/- 0.14 mJ). These unexpected preliminary results suggest at least two possibilities: 1) kangaroo rats use proximal muscles to replace the energy lost to the environment; 2) kangaroo rats do not loose energy when hopping on sand, but rather hopping mechanics are similar to hopping on hard surfaces.
