Elastic strain energy in the low back muscles during human walking.

A simple model of the thorax, pelvis and three columns of the intrinsic lumbar back muscles (= ILBM) was constructed. The model was used to study the length of the ILBM during the different stages of the walking cycle. The length of the right ILBM (especially the lateral column) was largest at right toe off, exactly the stage of the walking cycle in which most force was needed to prevent the torso from falling forwards and laterally.