Stability of the spine modelled as an arch

The erector muscles are frequently strained through improper lifting. Stability of the spine is maintained by the muscles, ligaments and pressures inside the body cavities. Modelling of this stability has been achieved using a new arch spine model developed using optimisation techniques. The position of the thrust line in the arch spine model can be used to analyse stability of the spine, and muscle forces introduced to change the position of this thrust line. The erector muscles move the thrust line forward to the centre line of the spine in a weight lifting task in a stooped posture. A method to calculate muscle forces stabilising the spine and to calculate internal forces in the vertebrae is presented. Calculations show that L3/L4 disc loads increase with muscle and ligament forces in the lumbar region.