Numerous mathematical models have been developed to investigate the high incidence of low back pain associated with lifting activities. These mainly consider the muscle forces required to support the spine, and few have considered the additional role of curvature. One previous model which represented the spine as an arch (Aspden 1987) indicated the curvature to have a significant effect on both loading and stability of the spine. However this model included collective loading patterns for body weight and muscle forces, and only partial representation of the spine. On the basis that the level of anatomic detail of a model affects the accuracy of its predictions (McGill and Norman, 1987), this thesis describes the development of a model which provides greater detail for investigating spinal stability in the sagittal plane. The curvature of the whole spine, a distributed loading pattern for body weight, and the activity of individual spinal muscle groups have been considered. Comparison with the previous arch model has shown these to be necessary features for determining the loading and stability associated with a given posture. In particular, application of individual muscle forces provide greater control of stability at each vertebral level. By considering the force requirements of the individual muscle groups and the consequent loads at each intervertebral joint, possible areas of tissue over load can be identified.