Individual muscle force estimations using a non-linear optimal design.

In order to estimate individual muscle forces during human movement a mathematically underdetermined system, representing the human musculoskeletal system, was solved using a non-linear optimization algorithm. The load sharing between muscles was made to depend upon the instantaneous contractile conditions of the muscles, a feature not incorporated in comparable non-linear optimal designs reported in the literature. The optimization algorithm was formulated as a convex system which guarantees a unique solution at the global minimum. The strengths and weaknesses of the present optimization algorithm were evaluated and compared to the classical algorithm reported by Crowninshield and Brand (J. Biomech., 14 (1981) 793-801).