[Role of A.A Ukhtomskiĭ in the development of the problems of work, working capacity and fatigue (peculiarities and characteristics of these states in various age periods)].

The data of research which has been carried out for years, are summarized. They are presented in a succession conforming to the A.A. Ukhtomsky views on the gradual enlargement of amplitude of muscles contraction, on capacity for work, and on fatigue. In the early postnatal period the phenomenon of gradual enlargement of amplitude of muscles contraction does not yet exist. It only appears after realizaiton of standing posture, when skeletal muscles transit from the type of tonic activity to the phasic--tetanic type. This phenomenon is due to that the first contractions induce hyperrelaxation which leads to the subsequent higher amplitude of contraction. The steady state of work capacity of neuromuscular system without any changes of amplitude, in the conditions of undisturbed circulation in the organism as a whole, can be maintained in all the periods of age for a long time without any signs of fatigue. This phenomenon takes place during the intervals between the contraction activity, the anabolic process having ample time to be completed. Such a form of work capacity is called stability. If the anabolic processes are unable to be completed during the intervals between the contractions, their amplitude gradually decreases reflecting the beginning of fatigue. The contractile activity which is going on during the fatigue state, is called endurance.