Low back muscle force prediction using activity surfaces and switching curves

An approach is described that displays the individual muscle force due to external loads as a surface called the muscle activity surface (MAS) in a multidimensional loading space. The independent loading variables spanning this space are determinants of the external loading in the lumbar plane of interest, thus decoupling the broad question of muscle load distribution from the specific details of a given loading task. The MAS of a given muscle yields the full muscle response to the external loading. It shows a threshold phenomenon, a preference for symmetric tasks, and a monotonic dependence on the flexion moment.<>