The Swing Phase of Locomotion

Abstract

Relatively little attention has previously been focussed upon the dynamics of the leg during the swing phase of locomotion, even though it is this phase which often presents the greatest problems for lower limb amputees. In this thesis an analogue computer simulation is developed which models the swing of a normal leg during locomotion. This simulation, which takes into account the polycentric nature of the knee joint, enables the change in length of the hamstrings to be studied and any desired muscle tension characteristic programmed for any swing duration. The importance of the ilio-psoas is shown, this muscle group providing a moment of approximately 20 Nm about the hip early in the swing phase at all speeds of locomotion. The maximum hamstring tension required late in the swing phase is approximately proportional to the speed of locomotion, being about 1.2 kN at a speed of 1.5 m/s. An energy balance is established relating the changes in potential and kinetic energy of the leg during the swing to the energy developed or absorbed by the main muscle groups, and again the variation with locomotion speed is studied. A minimum energy requirement is demonstrated at a locomotion speed of about 1.8 m/s if a stretch-storage process occurs in the hamstrings. Finally, a second analogue simulation is constructed to study the swing phase of an above-knee amputee using a conventional prosthesis. This simulation demonstrates some of the typical abnormalities of amputee gait. Its value as a design tool is shown by studying the knee moment required to be developed within the prosthesis. The essential contribution that this thesis makes to the study of locomotion is in demonstrating how analogue computation can yield quantitative results for trends previously only suggested qualitatively.