An integrated model of the neuromuscular system

A modeling framework for the neuromuscular system unifying five components is presented. The components are: (1) a biophysical model of the motoneuron pool predicting motor unit recruitment and motor unit firing times; (2) a biophysically based description of the excitation-contraction coupling in the sarcomeres, which determines the cross-bridge-cycling induced stress of a sarcomere; (3) action potential propagation along skeletal muscle fibers based on the monodomain model; (4) a continuum-mechanical, three-dimensional description of the muscle geometry including a realistic spatially-varying motor unit distribution for computing the deformations and the exerted force; and (5) phenomenological models of muscle spindles providing sensory feedback to the central nervous system. The individual components are strongly coupled to each other through a flow of information making a decoupled solution strategy of the different submodels impossible. The integrated model allows the simulation of the entire pathway from supraspinal input to force production enabling the investigation of various phenomena of the neuromuscular system, and the analysis of different physiological hypotheses.