Dudley S. Childress

The effect of pelvic list on the vertical displacement of the trunk during normal walking

Abstract We measured pelvic list in three normal ambulators, and calculated the vertical displacement of the trunk that is due to pelvic list. Pelvic list was found to be maximum at approximately toe-off and nearly neutral (less than 2°) at midswing for freely-selected gait. The effect of pelvic list on the vertical displacement of the trunk, for normal, freely-selected gait, was mainly to decrease the mean vertical position by 2–4 mm and shift the waveform in phase by about 10–15° lag. The magnitude of the trunks vertical excursion was determined to be virtually unaffected by pelvic list. This finding is in conflict with conventional wisdom that pelvic list reduces the vertical excursion of the body during normal walking.

The influence of four-bar linkage knees on prosthetic swing-phase floor clearance

ABSTRACT Four-bar linkage knees provide greater toe clearance during the swing phase of walking than do single-axis knees. The authors developed a computer model of a transfemoral prosthesis that allowed the kinematics of commercially available four-bar linkage knees and a single-axis knee to be simulated so legshortening could be characterized. A plot of hip-toe distance versus knee-flexion angle demonstrated fourbar knees are able to shorten the limb with less knee flexion than is needed using a single-axis knee. For a hip-knee angle combination at the time of minimum toe clearance during normal walking, contour plots revealed the four-bar knees have 0.9–3.2 cm greater toe clearance than do single-axis knees.

Two-dimensional representation of three-dimensional pelvic motion during human walking: An example of how projections can be misleading

We investigated the movements of skin markers located on the anterior and posterior surfaces of the pelvis during normal walking. Plots of the vertical versus horizontal displacements of the body-surface markers for a single gait cycle yield characteristic horizontal figure-of-eight patterns, often referred to as Lissajous figures. Some literature citations indicate that these figure-of-eight plots represent movement of the body center of mass in the plane perpendicular to the line of progression. We show evidence suggesting that the Lissajous plot for the body center of mass is U-shaped and that the observed figure-of-eight pattern is due to the location of the marker on the body surface coupled with pelvic rotation. A simple rigid-body model is used to demonstrate that pelvic rotation about the vertical axis can appear as horizontal translations in a planar projection. Even small rotations about the vertical axis are observable in the phase relation between horizontal and vertical displacements of surface markers in the projection. As a result, Lissajous plots of vertical versus horizontal displacements, particularly for points on the exterior of a rigid body, may be strongly influenced by rotations. We demonstrate that Lissajous patterns for the model are similar to patterns for the human pelvis during walking and that pelvic rotation has a large influence on Lissajous patterns (vertical movement vs medial-lateral) plotted from pelvic marker data. This demonstration illustrates how two-dimensional representations of three-dimensional movement can lead to incorrect interpretations.

Microprocessor based E.P.P. position controller for electric-powered upper-limb prostheses

A new extended physiological proprioception (e.p.p.) position controller for upper-limb prostheses, based on a microprocessor design is presented. E.p.p. and two controller configurations are discussed.

An investigation of tracking behavior exhibited during balancing and standing

A simple balance model, defined by a structure based on D.A. Winters (1995) concept of the passive mechanics of the body and a concept of manual control based on D.T. McRuers et al.s (1959) crossover model, was applied to different states of human upright standing. The model suggests that the velocity of the center of pressure is proportional to the acceleration of the center of mass, with a time delay. Three subjects performed standing tasks of different levels of difficulty in maintaining balance. These tasks were as follows: (1) standing quietly on both feet; (2) standing on one foot; and (3) standing with raised heels. The data were compared to the model. The time delay parameter of the model was determined with cross-correlation. Values of the time delay ranged from 200 to 450 ms. It is speculated that the range of time delay obtained from these events signify the range of adaptability of the healthy upright human body.