[Influence of physical training under conditions of 120-day simulated microgravity on contractile properties and musculo-tendinous stiffness of the triceps surae muscle].

The effect of a 120-day -5 degrees head-down tilt (HDT) bed rest with countermeasures (physical training) on the mechanical properties of the human triceps surae muscle was studied in four healthy young women aged 28.0. The results showed that the contractile properties of the skeletal muscle studied changed considerably. After HDT without countermeasures the maximal voluntary contraction (MVC) had decreased by 36% (P < 0.05), and the electrically evoked tetanic tension at 150 Hz (P) and isometric twitch contraction (P(t)) had decreased by 24% (P < 0.05) and 12 % (P < 0.05), respectively. Time-to-peak tension (TPT) of the twitch had significantly increased by 14% (P < 0.05), but half-relaxation time (1/2 RT), and total contraction time (TCT) had decreased by 19% (P < 0.05) and 18% (P < 0.05), respectively. The difference between P(o) and MVC expressed as a percentage of P(o) and referred to as force deficiency (P(d)), was also calculated. The P(d) had increased by 40% (P < 0.001). The rate of increase of voluntary contractions calculated according to a relative scale had significantly reduced, but for the electrically evoked contraction no substantial changes were observed. After HDT with countermeasures TPT, 1/2 RT and TCT had decreased by 4%, 7%, 19%, respectively in relation to the control condition. Training had caused a decrease of 3% (P > 0.05) in MVC, and P(t) and in P(o) of 14%, and of 9% (P > 0.05), respectively. The Pd had decreased significantly by 10% (P < 0.05). The rate of increase of electrically evoked tetanic tension did not change significantly during HDT with countermeasures but the rate of increase in isometric voluntary tension development was increased. Physical training provided a reserve of neuromuscular function, which attenuated the effect of bed rest. The experimental findings indicated that neural as well as muscle adaptation occurred in response to HDT with countermeasures.

[Contraction properties and musculo-tendinous stiffness of the human triceps surae muscle and their change as a result of a long-term bed-rest].

The effect of a 120-day 5 degree head-down tilt (HDT) bed rest on the mechanical properties and electromechanical delay (EMD) of the human triceps surae (TS) muscle was studied in four (mean age 31.5+/-1.7 yr) healthy young women subjects. The TS mechanical properties were evaluated based on the following indicators: maximal voluntary contraction (MVC), maximal strength (Po; frequency 150 Hz), peak twitch force (Poc), time-to-peak tension (TPT), half-relaxation time (1/2 RT) and tension development time to reach 25, 50, 75 and 90% of maximal tension. Force deficit (Pd) were estimated. In response to a light signal,the subject was supposed to make a voluntary foot flexion, with the instruction "to exert the fastest and greatest tension". EMD measurements were recorded from each subject during voluntary contraction. Surface electrodes sensed electromyographic (EMG) activity in the soleus muscle. A separate timer was used to determine total reaction time (TRT). Premotor time (PMT) was taken to be the time interval from the delivery of the signal to change in EMG. EMD was the time interval between the change in EMG and movement i.e. the time interval between EMG and the onset of muscle tension. After HDT Poe, MVC and Po decreased by 24.4, 36.1 and 11.5%, respectively, while Pd increased by 38.8%. TPT increased by 13.6%, while 1/2RT decreased by 19.2%. The rate of increase of voluntary contractions calculated according to a relative scale significantly increased, while the rate of development of electrically evoked contraction did not show any significant differences. The voluntary contraction EMD increased by 27.4%; PMT by 8.7%, and TRT by 13.6%. Thus, the mechanical changes suggest that weightlessness changes not only the peripheral processes associated with contractions but also the central and neural command. EMD is a simple and quick method for evaluation of muscle stiffness changes. Moreover, EMD can serve as an indicator of the functional condition of the neuromuscular system.

[Functional characteristics of human neuro-muscular system and their changes as a result of mechanical unloading of different duration].

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.

[Neuromuscular responses of the triceps surae muscle to prolonged passive stretch of the foot extensor muscles under conditions of simulated microgravity].

The effect of a 60-day 6 degrees head-down tilt (HDT) of bed rest with and without countermeasures on the mechanical properties of human the triceps surae muscle was studied in 12 healthy young men subjects. One group (n=6; mean age 30.8 +/- 3.1 years) underwent a 60-day HDT and a second group (n=6; mean age 30.5 +/- 1.9 years) underwent HDT with countermeasures (long-term passive stretching). The results showed that the contractile properties of skeletal muscle change considerably. After HDT without countermeasures the maximal voluntary contraction (MVC) declined by 33.5% (P < 0.05), the electrically evoked tetanic tension at 150 Hz (Po) and isometric twitch contraction (Pt) reduced by 18.0% (P < 0.02) and 17.3% (P < 0.05), respectively. Time-to peak tension (TPT) of the twitch increased by 3.4%, but half-relaxation time (1/2 RT) decreased by 7.2%, and total contraction time (TCT) increased not significantly. The difference between Po and MVC expressed as a percentage of Po and referred to as force deficiency (Pd), has also been calculated. The Pd increased by 61% (P < 0.001). The rate of rise of voluntary contractions calculated according to an relative scale significantly reduced, but the electrically evoked contraction no substantial changes were observed. After HDT with long-term passive stretching caused decrease by 43.0% (P < 0.05) in MVC, and Pt and in Po by 17.0%, and by 19.4% (P < 0.05), respectively. The Pd increased significantly by 100% (P < 0.001). TPT, and 1/2 RT not change significantly, and TCT of the twitch increased by 6.5%, respectively in relation to the control condition. The rate of rise of electrically evoked tetanic tension did not change significantly during HDT with countermeasures but the rate of rise in on isometric voluntary tension development were decreased. These data indicate that prolonged passive stretching of a single muscle decreases voluntary strength. Thus, the received data specify, that the long passive stretching of a muscle does not find out preventive facilitate contractile properties of the muscular device from negative influences of mechanical unloading. This study presents evidence that prolonged passive muscle stretching can lead to some modification of contraction material behavior. In addition, altered material properties seem to affect proprioceptive feedback and, therefore, the motor unit activation in proportion to the contractile failure.

[Studies of the architecture and functions of human skeletal muscles with the use ultrasonic scanning].

Architecture of m. triceps with the neutral ankle positioning (O degrees) was studied in vivo in essentially healthy male subjects (n = 8) and patients with motor disorders of varying etiology (4 males and 4 females). Ultrasonic scanning produced real-time images of m.gastrocnemius medialis, m. gastrocnemius lateralis and m.soleus both during relaxation (passive state) and isometric effort at 50% of maximal voluntary force (active state). Length, myofiber pinnation angle and muscle thickness were measured.

[Skeletal muscle reaction in man to a decrease in gravitation]. / Reaktsiia skeletnoi myshtsy u cheloveka na snizhenie gravitatsii.

Functional characteristics the triceps surae muscle were studied in sex subjects exposed for 7 days to decreased unweighting induced by "dry" immersion (DI). After DI, the maximal voluntary contraction was a significant reduced by 33.8%, and the electrically evoked tetanic contraction (Po), and the twitch tension (Pt) was not significantly changed (8.2 and 9.9%, respectively). The force deficiency increased by 44.1% (P < 0.01). The twitch time-to-peak did not change, and to half-relaxation decreased by 5.3%. The Pt:Po ratio was decreased by 8.7% (P < 0.01) after "dry" immersion. The muscle surface action potential increased by 18.8% (P < 0.01), and a decrease of the amplitude and the area by 14.6% (P < 0.05), and 2.8% (P < 0.01), respectively. A comparison of the electrical and mechanical alterations recorded in the muscle suggests that due to decreased functional demands there may be an alteration not only in peripheral processes associated with the contraction, but also in the central (motor) command to the acting apparatus. We suppose that among peripheral sites, intracellular processes of contraction play the major in the contractile impairment recorded during "dry" immersion.

[A comparison of the contractile properties of the muscles of the lower extremities in man]. / Sravnenie sokratitel'nykh svoistv myshts nizhnikh konechnostei u cheloveka.

The physiological features of two antagonistic muscle groups, the dorsiflexors and plantar flexors of the ankle, have been compared in 11 healthy subjects aged 15-17 years (+/- SE; 16 +/- 1.2 years). Contractile properties of plantar flexors of the foot, namely of tibialis anterior (TA) and extensors triceps surae (TS) have been estimated by mechanical parameters of voluntary and electrically evoked contractions. All test subjects exhibited tolerance to supramaximal force of electric stimulation of n. tibialis and n. peroneus profundus at a frequency of 150 impulses.s-1 (for TS) and 150 impulses.s-1 and 250 impulses.s-1 (for TA). TA displayed high velocity and force-velocity properties (p < 0.05-0.001); TS had high force parameters (p < 0.05-0.01). The magnitude of force deficiency observed during voluntary contraction of these muscles is lower in TA and higher in TS (p < 0.05). The results permit supposing that differences in contractile properties of the muscles under study depend on a various specific contribution of peripheral and CNS factors.

[The effect of long-term bed-rest head-down-tilt hypokinesia on the functional properties of the human neuromuscular apparatus]. / Vliianie dlitel'noi postel'noi antiortostaticheskoi gipokinezii na funktsional'nye svoistva nervno-myshechnogo apparata u cheloveka.

An influence of 120-days antiorthostatic (-6 degrees) hypokinesia (ANOH) on the functional properties of human m. triceps surae (TS) was investigated. After ANOH the maximal force and the maximal voluntary contraction of TS decreased on the average by 45.5% and 33.7%, respectively, and the maximal twitch response force--by 36.7% (P < 0.05-0.01). The value of force deficit increased on the average by 60.2% (P < 0.001), while a relative increase of the TS force contraction decreased in response to pair irritation (P < 0.05-0.01) as well as the velocity properties of TS after ANOH (P < 0.05-0.001). The rate of absolute (c.u.) tension development fell significantly in response to electrical nerve irritation and during voluntary contraction, while the force-velocity muscle properties according to relative (%) parameters remained unchanged. The fatiguability index of TS constituted the average 0.61 +/- 0.02 after ANOH as against 0.80 +/- 0.03 prior to it (P < 0.05). It is postulated the alterations of contractile properties of TS are due both to atrophic processes, muscle length change, condition of sarcoplasmic reticulum and to changes in the state of the central nervous system.