Improved description of controlled movement of the upper limb at activation of the skeletal muscle

A new, refined description of the controlled movement of the basic elements of the human musculoskeletal system in the process of activation of skeletal muscles has been developed, taking into account the viscosity and nonlinear viscoelasticity of muscular and connective tissues. As a basis, the three-element model of skeletal muscle, previously proposed by the authors, consisting of a nonlinearly viscoelastic element describing the deformation of the muscle shell, was used; a nonlinearly elastic element describing the deformation of actin and myosin filaments with a contraction of the muscle, and a contractile element formalizing the actomyosin interaction were used too. In order to adequately simulate the equivalent traction formed by the muscle and connective tissues, a nonlinearly viscoelastic element that deforms the tendon is connected to the three elements listed above. For approbation of the proposed biomechanical model, the lifting of the load by the upper limb (arm) of a person is analyzed. The performed calculations have shown the possibility of describing the phenomena of the "delay" of the onset of motion when the muscle is activated and the dying oscillations of the links of the musculoskeletal system occur near the equilibrium state. In the example considered, the value of the "delay" was 0.08 s, and the period of the angular oscillations was 0.55 s, respectively. At t > 1.5 s, oscillations practically cease. In addition to rationalizing sports training and work activity, the developed model and calculation method are of interest for the reproduction of muscle activity in polymer "smart" materials used in the creation of intelligent drives and controlled configuration designs.