DEMES, Brigitte; CARLSON, Kristian J.; FRANZ, Theresa M.; Stony Brook University; Stony Brook University; Stony Brook University: The dynamics of lemur turns

Maneuverability is an important, yet understudied, aspect of locomotion in arboreally adapted animals, as substrate properties require frequent turns. This is a first attempt to quantify the forces involved in turning. Substrate reaction forces were collected for several individuals of Lemur catta performing turns on a force transducer integrated into either a wooden runway or an elevated pole. Limb contacts at the onset of turns were analyzed. Animals turn with moderate lateral flexion of the trunk. The change in direction of the linear velocity vector is primarily accomplished by a lateral push of the limbs at the outside of the turn, in particular the outer hind limb. Angular acceleration for trunk rotation is generated by horizontal impulse torques of several limbs. The outer hind limb is again of particular importance, with a propulsive impulse rotating the animal in the direction of the turn that is at least an order of magnitude higher than any of the impulses of the other limbs. Impulses and impulse torques opposite to the direction of the turn do occur. Inner and outer limbs do not differ in peak vertical forces; i.e., the animals are not leaning into the turn. Mediolateral forces and impulses are higher for the turns than for linear progression, similar in magnitude to the fore/aft forces, and they are more consistent in their direction. A steeper turning angle on the ground is associated with higher mediolateral forces than a shallower angle. Average speed when turning is slower than the speed in linear progression. Forces associated with turning behaviors are sufficiently different from those of linear locomotion to deserve attention when characterizing the dynamic environment of limbs. Supported by NSF BCS 0411489