Systems are analysed which consists of connected in parallel or series contractile (reactor-Rc) and elastic (elastic body-EB) parts similar to Kelvin or Maxwell's rheological models and to sarcomeres of the insect flying muscle (IFM) or vertebrate skeletal muscle. The feedback takes place if EB is a deformable sorbent of the mobile activator or inhibitor (effector--E) of the mechanochemical process proceeding in Rc. The condition of oscillative instability of mechanical rest was found for the system of the parallel type. This condition requires that E migration in the system Rc--EB braught about contraction (lengthening) of EB simultaneously with an increase (weakening) of the stretching force on EB from Rc. The oscillation frequency nu satisfies approximate ratio nu approximately less than DL-2 (where D--E diffusion coefficient, L--typical distance between Rc and EB), corresponding to specific frequencies in IFM. An automatic correction of the process in Rc is possible for the system of the serial type in order to increase useful mechanical power. Such a correction is achieved when a series elastic component contracts while absorbing E, if E is the process activator in Rc.