Функциональные свойства нервно-мышечного аппарата человека и их изменения в результате механической разгрузки разной длительности

Abstract

This study examined the effects of short- (1-, and 3-day) and long-term (7-day) 'dry' immersion (DI) on neuromuscular function of human the triceps surae muscle. The isometric twitch tension (Pt) decreased by 8.7% after 1-days, but increased by 11.5 and 9.8 % after 3- and 7-days DI, respectively. Maximal voluntary contraction (MVC) decreased by 13.6, 19.7, and 33.8% after 1-, 3-, and 7-days DI, respectively (p < 0.05-0.01), electrically evoked (frequency of 150 impulses x s(-1)) tetanic tension (Po) reduced by 1.8, 5.3, and 8.2%, respectively, (nonsignificant). The difference between Po and MVC expressed as a percentage of Po and referred to as force deficiency (Fd) was also calculated. Fd increased by 23.4, 20.2, and 78.7% after 1-, 3-, and 7-days, respectively (p < 0.05-0.001). After DI, the time-to-peak tension (TPT), half-relaxation time (1/ 2 RT), and total contraction time (TCT) was reduced. The TPT decreased by a mean value of 8.5, and 3.3% after 1- and 3-days, respectively, and after 7-day did not reveal significant changes in the curve of the TPT. 1/2 RT and TCT was shorter in the post-immersion condition than in the control value. The rate of increase of voluntary contraction calculated according to relative scale was significantly reduced after DI (p < 0.05-0.001), but for the electrically evoked contraction (frequency of 150 impulses x s(-1)) there were no substantial changes from the initial physiological state. A standard 2-min fatigue of electrically-induced intermittent test (frequency of 50 impulses x s(-1)) did not differ substantially from the initial physiological state, but the electrical M-waves reduced significantly. The relative extent of the decline in either of these two parameters can be determined from the change in the relation of the electrical M-wave to the contractile response (the E/C ratio). After long-term DI (7 day) of muscle a significantly greater decline of electrical waves is observed as compared to contractile response by a short-term DI (1-, and 3-day), respectively.