The consequences of lateral curvature for the laterally curved lumbar spine were analyzed in a static 3-D biomechanical model. The model used published anatomical data for the positions of the vertebrae and for the muscle insertions and muscle maximum contractile force. It was initially symmetric about the sagittal plane. Subsequently, three dimensional measurements of the spines of patients with lumbar scoliosis (mean Cobb angle 38° ) were used to create a new geometry representing the asymmetry of lumbar scoliosis. The model was used to calculate the maximum values of efforts in the three principal directions applied to the T12 vertebra, and subject to the following constraints: equilibrium of forces and moments acting on all vertebrae, muscle forces > 0, and less than a physiological maximum proportional to their cross-sectional area, and motion segment displacements due to elastic deformations. The maximum efforts were a linear function of the variables (muscle forces and joint forces) so linear programming was used to solve this indeterminate problem. The findings indicated that the overall magnitudes of effort for the three principal directions of effort would not change much in the presence of the spinal curvature. Asymmetric muscle activity would be necessary to perform these efforts, but the total activity (force) of all muscles would not differ much. However, the motion segments of the spine would be more symmetrically loaded in the scoliosis spine than that symmetric in the sagittal plane. This asymmetric loading may contribute to the progression of scoliosis by producing asymmetric growth in young patients, and asymmetric remodelling in skeletally mature patients.