A three-dimensional static torso model for the six human lumbar joints

Abstract

A simple three-dimensional static torso model for the prediction of the force distributions at the six human lumbar levels in different activities was developed. There are two procedures involved in the model calculations, the intersegmental resultant joint forces and moments of the presumed 26 joints and the internal muscoloskeletal force distributions of the 6 intervertebral disc joints. In formulation of the joint force distribution problem, 6 muscle forces and 3 moment equilibrium equations at one of the six disc joints (e.g., L3/L4) with muscle stress (muscle force divided by physiological cross sectional area - PCSA) upper limits were used. The disc compressive force was minimized as the cost function of the linear programming to solve the force distribution problem. This solution of disc force distribution was further substituted into the next level. Such sequential substitutions of joint level's force equilibrium equations were used to solve for the disc forces at all 6 joint levels.