The mechanism of gradation of muskulyatorny tension is an important factor of increase in muscular force. The leading mechanism changing the size of muscular tension is character of a nervous impulsation. As it was already told, with increase of size of manifestation of force the frequency of fluctuations of one neuromuscular unit can increase with 5 – 6 to 35 – 40 fluctuations a second, and it is proportional to the developed kinetic energy, and as for total activity of a muscle, it increases to a certain limit.
curve force speed. It is possible to believe that this dependence reflects the same properties, as previous. The considered curve can be expressed by the so-called main equation of muscular contraction offered by A. Hill:
Only at distinction of threshold values amplitude of currents of action can increase because of non-simultaneous inclusion in work of separate fibers. As for electroactivity of all strained muscle, it also increases in process of growth of size of its tension, but to a certain limit.
When performing the movements which are not demanding manifestation of the maximum muscular force for dispensing of muscular tension other mechanism is used. In this case the highest nervous centers determine generally necessary sizes of spatial, temporary and high-speed parameters of the movement. As for the necessary combinations of muscular tension, it is carried out by more low located nervous departments. It is known that the effector impulsation comes at first not to muscle fibers, and to the muscular device of muscular spindles that leads to change of tension in them and the corresponding excitement of their receptor device. Further regulation is carried out according to the scheme of a miotatichesky reflex.