Responses of knee extensor muscles to leg press training of various types in human.

Responses of m. vastus lateralis to 8-week resistive training of various types at leg press mashine were investigated in 30 male subjects. Training loads were 25, 65 and 85% of one repetition maximum for low (LI), medium (MI), and high intensity (HI) training groups respectively, while angular velocities of contraction differed considerably between groups. The total work done during training session was identical. The maximum strengths during isokinetic knee extension in LI and HI groups were increased at most angular velocities. In group MI increments were obtained only during concentric contractions. Significant improvement of fatigue resistance and maximum oxygen consumption (V(O2max)) was seen only in group MI and LI, respectively. The training-related increase of cross-sectional area in type II fibers in m. vastus lateralis was in the order of HI > MI > LI group, and that of type I fibers was opposite. The increased myonuclear number was found for HI group. The data suggest that fiber hypertrophy, fatigue resistance and V(O2max) changes were related to the type of training.

[Optimization of training: development of a new partial load mode of strength training].

Hypertrophic effect of strength training is known to originate from mechanical and metabolic stimuli. During exercise with restricted blood supply ofworking muscles, that is under conditions of intensified metabolic shifts, training effect may be achieved with much lower external loads (20% of one repetition maximum (1 RM)). The aim of the study was to compare the effects of 8 wks high-intensity (80-85% MVC) strength training and low-intensity (50% 1 RM) training without relaxation. The high-intensity strength training leads to somewhat higher increments in strength and size of trained muscles than training without relaxation. During high-intensity training an increase of area occupied by type II fibers at muscle cross section prevails while during training without relaxation - an increase of area occupied by type I fibers takes place. An exercise session without relaxation leads to a more pronounced increase in secretion of growth hormone, IGF-1 and cortisol. Expression of gene regulating myogenesis (Myostatin) is changed in different ways after high-intensity strength exercise session and after exercise session without relaxation. Low-intensity strength training (50% 1 RM) without relaxation is an effective way for inducing increases of strength and size of trained muscles. This low intensive type of training may be used in restorative medicine, sports and physical culture.

[Evaluation of training efficacy for improving maximal voluntary contraction without noticeable hypertrophy].

The aim of the study was to estimate efficiency of the strength training protocol designed to improve maximal voluntary contraction without development of muscle hypertrophy. The principal difference between chosen training protocol and classical strength training was that the number of training movements during training session was increased to improve the motor skill, and rest periods between the training movements were increased as well to minimize damage of muscle fibers, which is one of the factors inducing muscle hypertrophy. Knee extensors of right leg in 11 physically active males were trained 4 times a week for 4 weeks. Evaluation of force-velocity characteristics with simultaneous recording of EMG-activity was performed in both trained and untrained legs immediately before, during and several times after the 4 wks training period. Before and after training the size and contractile properties ofipsi- and contralateral knee extensors were evaluated by MRI and twitch interpolation technique. Maximum strength gains after 4 week of training were about 17% in both trained and untrained legs and did not differ significantly from each other. A noticeable increase of EMG-activity during contraction was also found for both legs after 4-wks training period. The observed changes were not accompanied by any significant changes of muscle size, demonstrating the "neural" nature of the training effects.

[Acute effects of eccentric work on a bicycle ergometer].

The dynamics of delayed onset of muscle soreness after exercise on an electrically driven cycle ergometer with floating seat under preferentially concentric and eccentric conditions (forward and backward rotation of the pedals) has been evaluated using three different tests. The delayed onset of muscle soreness was determined using three different procedures: two with active contraction of the tested muscle group in multi-joint (going downstairs) and single-joint (knee extension) movements and one with passive pressure applied to the central part of m. vastus lateralis. With the use of two active tests, the maximum delayed onset of muscle soreness was recorded on the 1st-3rd days after intensive bicycle exercise without significant differences between the groups. Under conditions of passive testing, a tendency to a slower development (both an increase and a decrease) of delayed onset of muscle soreness was recorded. A positive correlation between the relative tension and the delayed onset of muscle soreness was found. Relative tension was determined as a decrease of strength during recovery related to the initial level. No relationship between volume/duration of exercise and the delayed onset of muscle soreness was found.

[Physiological effects of using the low intensity strength training without relaxation in single-joint and multi-joint movements].

The effects of classical strength training (CT) and low intensity strength training without relaxation (TwR) upon size, strength and fatigability of leg muscles in men were compared. A 8-10-week strength training led to an increase of size and maximal voluntary contraction of trained muscles. After the CT, the increment of strength was higher; on the other hand, strength increments related to total work performed increased after the TwR noticeably higher than after the CT. Two training programs influenced the size of total muscle and of muscle fibers (MF) differently: the volume of m. quadriceps femoris increased more after the CT than after the TwR. The CT induced a significant increase of cross sectional area (CSA) of fast MF, and the TwR induced an increase of CSA of slow MF. Resistance to fatigue after the TwR was higher than after the. The effects of TwR were more pronounced in single-joint movements training than in multi-joint movement.

[Creatine as a metabolic controller of skeletal muscles structure and function in strength exercises in humans. The cellular mechanisms].

The effects of creatine oral supplementation combined with a 10-week resistive training of morphometric, contractile and molecular characteristics of human vast lateral muscle fibers were studied. 2 groups consisting of 9 young healthy men each were involved in resistive training of knee extensors for 10 weeks. Volunteers of the first group received per os 20 g of creatine for the 1st week of training and 5 g for the rest of the experimental training period. We found a significant increase of slow and fast-twitch fiber size in both trained groups and a significant increase of Ca-sensitivity of skinned single fiber contractility in creatine-supplemented group. The serum creatine phosphokinase activity in blood samples taken 24 hours after exercise session increased in all stages of the experimental training in both groups. At the same time, the adaptive decrease of the after-exercise CK concentration was observed in the placebo but not in the creatine-supplemented group. The altered integrity of the subsarcolemmal dystrophin layer was revealed in both groups after training.

[Creatine as a metabolic controller of skeletal muscles structure and function in strength exercises in humans].

The aim of study was to investigate the effect of oral creatine supplementation upon muscle performance and aerobic capacity of the organism. Knee extensor muscles of two groups with 9 subjects in each were subjected to strength training with and without creatine supplementation (Cre and Pla) for 10 weeks, three times a week with an effort of up to 85% of maximal voluntary contraction (MVC). The Cre group received 5 g of creatine monohydrate a day. After 10 weeks strength training, an increase of MVC by 29 and 40% in training (isotonic) regimen was recorded for the Pla and Cre groups respectively. The muscle isokinetic torque increments of 10-11% were obtained in the Pla group at angular velocities corresponding to training velocities, and in the Cre group increments of 11-17% were recorded at all angular velocities tested. No changes were found in the fatigue test by the Pla group, whereas Cre group showed a tendency for an increase. The aerobic and anaerobic capacities of the organism did not decrease in both groups. Thus the creatine supplementation during strength training potentates an increase of force-velocity characteristics of trained muscle group without impeding aerobic capacity of the organism.

Effect of dry immersion in combination with stimulation of foot support zones upon muscle force-velocity characteristics.

The complex of motor disturbances arising under conditions of real and simulated microgravity that include decrease of contractile characteristics of postural muscles is likely to be a result of withdrawal of support stimuli. Artificial stimulation of support zones of feet is shown to diminish partially or prevent completely the negative effects of microgravity on the motor system. The aim of the study was to evaluate and compare the changes of contractile properties of extensors and flexors of knee joint measured in isokinetic and isotonic regimes under conditions of simulated microgravity (7 days dry immersion).

Mechanic stimulation of the soles support zones as a countermeasure of the contractile properties decline under microgravity conditions.

Decrease in muscle contractility is an inevitable consequence of exposure in microgravity. A wealth of currently accumulated facts is indicative of profound modifications in structure and function of the skeletal muscles in the absence of gravity. Investigations with humans during space flights of varying duration (L.I. Kakurin et al., 1971; I.B. Kozlovskaya et al., 1984, 1987, 1991;.), ground-based simulation studies (A.M. Genin et al., 1969; L.S. Grigorieva et al., 1983), and numerous experiments with animals (E.I. IIyina-Kakueva et al., 1979; O.M. Edgerton et al 1991; B.S. Shenkman et al., 1994) made it evident that removal of gravitational loading is fraught with significant reductions in the contractile properties of muscular fibers, especially noticeable in muscles-extensors. Results of ground-based simulation studies led to the hypothesis that changes in muscle contractility developing already after few days in microgravity conditions are consequent to reduction in support afferentation that plays an important role in initiation and maintenance of the activity of tonic motor units (A.V. Kirenskaya et al., 1986). In view of the above, an idea has been proposed to prevent losses in tonic muscles contractility by application of artificial support. Testing of this hypothesis was the theme of the present investigation.