Biomechanics and dynamics of turning

Abstract

In chapter one, I examine the extent to which a pelagic marine gastropod, Clione limacina, turns by changing its wingstroke kinematics versus shifting its tail position as a rudder. I find that there is no evidence for tail-ruddering in free-swimming animals under the conditions tested. In response to tilting a tethered animal with respect to gravity, however, the wingstroke kinematics do change. Compared to its preferred head-up orientation, when the animal is tethered at 45° or 90°, the average wing position shifts ventrally by one body width.In chapter two, I explore the effects of turning around a 90° corner for humans with and without lower-limb, below-knee amputations. I find that amputees appear to compensate for their limb loss by reducing the extent to which they shift their prosthetic limbs under their pelvis during a turn. I also find that there is no difference between intact and amputee subjects in the distribution of the body's total rotation between the two feet.In chapter three (Flick, et al., 2005), we compare the mechanical performance of prosthetic rotation adaptors to data on ankle rotation in intact humans. We find that the human ankle varies in composite stiffness throughout the stride. While none of the rotation adaptors tested varies its stiffness in the same pattern, most of them encompassed the range of human ankle rotation and torque.In chapter four, I use a finite element model of the below-knee amputee's residual limb and prosthetic socket to predict the differences in tissue strain between walking straight and turning, both with and without a prosthetic rotation adaptor. There are differences in the absolute amounts of tissue strain and its rate of increase between walking straight and turning. The inclusion of a rotation adaptor has very little effect.