LAMMERS, A R; EARLS, K D; BIKNEVICIUS, A R; Ohio University: The effects of substrate diameter on locomotor biodynamics in gray short-tailed opossums (Monodelphis domestica)

The effects of substrate diameter (contour) on locomotor biodynamics were studied in the gray short-tailed opossum (Monodelphis domestica). Two horizontal substrates were used: a flat trackway with a force platform integrated into the surface and an cylindrical trackway (20.3 mm diameter) with a force-transducer instrumented region. On both flat and curved substrates, forelimbs exhibited higher dorsoventral (DV) impulse and peak force than hindlimbs. Although DV impulses were lower on the flat substrate than on the arboreal, this was most likely due to speed effects because the animals, on average, ran faster on the flat trackway. Furthermore, forelimbs were consistently net braking and hindlimbs net propulsive. A sharp contrast was found in the mediolateral (ML) forces: net ML impulse measures indicate that limbs exert net lateral forces on flat substrates (greater in forelimbs than in hindlimbs) whereas medially directed limb forces were found on the curved surface (no difference between limbs). These results bear significance for understanding the roles of limbs in locomotion on terrestrial and arboreal substrates. High medially-directed limb forces found in the highly curved (arboreal) trackway increases the friction force, while the lower speeds cause lower peak DV forces to be generated. Thus, the sheer component is reduced. Medially-directed and equivalent fore- and hindlimb forces, together along with decreased speed, allows these small mammals to safely move on narrow substrates. (Supported by NSF 0080158)