Mathematical modelling is widely used in the field of biomechanics. The traditional
approach to investigate spine related injuries is to check the strength of the
components of the spine. Spinal stability approach focuses on the force polygons
formed by the body weight, muscle forces, ligament forces and external load. This
force polygon is expected to stay within the boundaries of the spine to ensure stability.
Proving the possibility of one force polygon within the spine boundaries proves the
stability of the spine.
This study focuses on the full curvature of the spine for spinal stability investigations
in a lifting activity. An experiment has been designed to investigate the postural
differences in males and females by measuring the full spinal curvature with a skin
surface device. Distributed body weight force, with increased detail of muscle and
ligament forces acting on the spine have been modelled by writing a code in Visual
Basic, while lifting a load from the boot of a car in the sagittal plane. This model is
flexible enough to reflect changes in body weight parameter.
Results show that there is a difference between male and female postures during the
full span of lifting activities. Application of individual muscle forces provides greater
control of stability at each vertebral level. By considering the elongation of the
ligaments and the force requirements of the muscle groups, it is possible to diagnose
soft tissue failure. The differences in posture result in different moment arms for
muscles and ligaments causing different loading on the spine. Most critical postures
have been identified as the fully flexed postures with external load acting on the spine.
Conceptual design ideas have been proposed to assist lifting a load from the boot of a
car to eliminate the excessive flexion and loading on the spine.
Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.