Spine modelling for lifting

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.