A FINITE-ELEMENTS APPROACH TO THE STUDY OF FUNCTIONAL ARCHITECTURE IN SKELETAL-MUSCLE

A mathematical model that simulates the mechanical processes inside a skeletal muscle under various conditions of muscle recruitment was formulated. The model is based on the finite-elements approach and simulates both contractile and passive elastic elements. Apart from the classic strategy of solving shape deformation of elastic structures by a finite-elements approach, an algorithm was formulated to account for the volume-preserving properties of muscle tissue. This combinatorial approach has two advantages over previous attempts to model skeletal muscles. First, no assumptions had to be made on the shape of any of the muscle components (e.g., muscle-fiber curvature), and second, different levels of recruitment for motor units can be simulated. The possibility of calculating pressure distribution inside the muscle is intrinsic to the method used. Some studies of unipennate and bipennate muscles show that external muscle shape and pressure distribution depend on the pattern of recruitment used and the elastic nature of the surroundings of the muscle. More homogeneous distribution of activated motor units produces less shape deformation compared to the passive state, and the final force output is reached more rapidly after the onset of recruitment. Finally, we suggest that complex and serial arrangement of motor units, as well as certain geometric patterns of motor endplates can be explained with this type of model in the light of temporal force production