Locomotor kinetics on sloped arboreal and terrestrial substrates in a small quadrupedal mammal.

Small animals must be capable of moving on a wide variety of surfaces; thus, examining the mechanics of locomotion on a wide variety of substrates is necessary to understand how the animal can utilize its habitat. Therefore, locomotor kinetics are examined on arboreal and terrestrial sloped substrates in the marsupial Monodelphis domestica (gray short-tailed opossum). Substrate reaction forces were measured as opossums moved across four trackways: 30 degrees upslope and 30 degrees downslope trackways, which were flat ("terrestrial") or cylindrical ("arboreal"). Regardless of substrate slope, medial limb forces were measured on arboreal trackways and usually lateral limb forces on terrestrial trackways. Otherwise the general patterns of vertical and craniocaudal forces and impulses were similar between same-sloped terrestrial and arboreal trackways. Some significant modifications to these gross patterns occurred: on the arboreal upslope trackway, hindlimbs supported more body weight than on the terrestrial uphill, possibly because hindlimbs were more stably positioned on the upslope arboreal trackway than forelimbs. Furthermore, the difference between fore- and hindlimbs with respect to craniocaudal impulses was less on the arboreal sloped trackways. In conclusion, kinetic patterns can usually be explained by body weight support roles and by the placement of the limbs on the arboreal trackway.