Effects of support stimulation on human soleus fiber characteristics during exposure to "dry" immersion

In this study the model of 7-day dry immersion (DI) was used. 17 male volunteers (23-29 years old) were divided in 2 groups: (i) 7-day DI without support (DI, n=9), (ii) 7-day DI using support stimulation (DIS, n=8). Support stimulator device exerted pressure of 0.2 +/- 0.15 kg/cm2 upon the plantar support zones simulating the walking pattern 6 times a day for 20 minutes of every hour: 10 minutes at a speed of 75 steps/min and 10 minutes at a speed of 120 steps/min. M. soleus biopsy was performed before and immediately after DI. The m. soleus fiber myosin heavy chain (MHC) profile, myofiber cross-sectional area (CSA) and total protein concentration were analyzed in frozen serial sections. In addition, NO-synthase 1 (NOS1) levels indicative of normal muscle cell signaling were analyzed by western blotting in 4 persons in each group. After dry immersion, percentage of muscle fibers containing type I MHC decreased by 6% (p<0.05) in group DI, but was not changed significantly in group DIS. Percentage of the type IIa fibers was significantly altered in none of the groups. Type I fiber CSA decreased by 24.4% (p<0.05) in group DI. No significant changes of type I fiber CSA were found in group DIS. CSA of the type IIa fibers significantly altered in none of the groups. The total protein concentration was found increased by 17.6% in group DI and by 21% in group DIS. The increased total protein content in group DI suggests a diminution of fiber CSA attributed to the loss of non-protein component of fibers. NOS1 decreased by 35.6% in group DI and increased by 58.1% in group DIS. We conclude that 7 days in dry immersion lead to reduction in the type I muscle fiber percentage, loss of the non-protein component and decline in NOS1. These changes were clearly prevented by the support stimulation protocol applied during the DI period.     

Magnetic resonance tomography measurement of the thigh adipose tissue volume in men

The volume of the thigh adipose tissue was estimated using magnetic resonance tomography (MRT) and anthropometric measurements. Eighty-seven physically well-developed men aged 18–45 years participated in the experiment. The MRT estimate of the thigh fat volume was 2206 ± 882 cm³. The results were used to derive two multiple linear regression equations for calculating the thigh adipose tissue volume from anthropometric parameters. The correlation coefficient between the thigh adipose tissue volumes calculated from the equation and measured by MRT was r = 0.97.     

Final blood lactate concentration after incremental test and aerobic performance

The goal of this study was to test the hypothesis that, in groups of highly trained endurance athletes (first and junior national teams), the final blood lactate concentration at maximum aerobic performance decreased as their training status increased. This study was performed with 20 physically active volunteers and 45 highly trained middle- and long-distance endurance athletes (speed skaters, triathletes, and cross-country skiers). Significant negative correlations (r = ?0.59 to ?0.87) between the final blood lactate concentration after incremental tests until exhaustion and aerobic performance (anaerobic threshold (AT)) were found only for the groups of highly trained endurance athletes, but not for the group of physically active subjects. It was shown for highly trained speed skaters that the final lactate concentration in their blood decreased and the oxygen consumption at AT increased with an increase in the volume of type I muscle fibers in the working muscle (r = ?0.84 and r = 0.7, respectively).     

Effects of chronic low-frequency electrical stimulation of human knee extensor muscles exposed to static passive stretching

The study investigated the effects of chronic low-frequency electrical stimulation (CLFES) of the stretched knee extensor muscles versus CLFES without a resistance load. A total of 19 male volunteers were randomized into two groups with similar aerobic and force-velocity properties. In group 1, anterior thigh muscles (the knee extensors) of both legs were exposed to CLFES (15 Hz). In group 2, the CLFES of the knee extensors was combined with stretching. The stimulated subjects demonstrated a marked tendency towards increasing endurance and a significant increase (by 10%) in both succinate dehydrogenase activity and the percentage of muscle fibers containing slow myosin heavy chain (MHC) isoforms. At the same time, the proportion of fibers reacting with the antibody against fast MHC isoforms decreased by 12%. In group 1, the maximum voluntary force (MVF) significantly decreased, the volume of m. quadriceps femoris (as measured by magnetic resonance imaging) remained unchanged, and the size of the fast fibers slightly decreased (by 11%). In group 2, no significant decrease in the MVF was observed, while there was a significant increase in muscle volume and the cross-sectional area of muscle fibers.     

Human soleus fibers contractile characteristics and sarcomeric cytoskeletal proteins after gravitational unloading. Contribution of support stimulus

The effects of support withdrawal and support stimulation on the contractile characteristics of human soleus fibers and cellular factors which influence them were studied. The experimental model of the "dry" head-out water immersion was used in the study. In this model, the hydrostatic pressure on different sites of the body surface are equal so that the experimental conditions are close to the complete supportlessness. A 7-day exposure to dry immersion resulted in a decrease in the maximal isometric tension of the skinned fibers, a decline in the myofibrillar Ca2+-sensitivity, and the relative loss of the titin and nebulin content. A significant decrease in the percentage of fibers containing slow myosin heavy chains was also observed after dry immersion. The application of the mechanical stimulator influencing the plantar support zones with a pressure of 0.2 +/- 0.15 kg/cm2 6 times a day for 20 minutes of each hour brought about a complete prevention of the above listed effects of dry immersion. The data obtained allow one to conclude that the decline in maximal tension and Ca2+-sensitivity as well as myosin shift and loss of sarcomeric cytoskeletal proteins are associated with the support withdrawal during the exposure to dry immersion.     

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.     

Aerobic capacity and force-velocity characteristics in cross-country skiers at the end of preparatory period and at the beginning of period of competitions

The goal of this study is to compare the dynamics of aerobic and force–velocity characteristics of the shoulder girdle muscles and leg muscles during high-volume aerobic training in junior cross-country skiers in the time interval from the end of the preparatory period to the beginning of the competition period. Eleven junior cross-country skiers were repeatedly tested from December to February. In this period, the volume of aerobic training was 22–23 h per week. During the experimental period, the knee extensors torque in the range of angular velocities of 30–300 degrees/s was observed to decrease, with no changes in the volume of the quadriceps muscle of thigh and knee flexor muscles. The maximal oxygen consumption rate (VO₂ max) was observed to decrease by 6% (P < 0.05) in the treadmill test, while the oxygen consumption at anaerobic threshold (VO₂ at La = 4 mmol/L) was unchanged. On the contrary, the functional capacity of the shoulder girdle muscles was enhanced. The force-velocity characteristics of the shoulder girdle muscles that were estimated in the maximal anaerobic power test at a double poling ergometer increased by 16% (P < 0.01), and the volume of the triceps muscle of arm increased by 4.6 (P < 0.01). The aerobic capacity of the shoulder girdle muscles that were estimated by the VO₂ at La = 4 mmol/L increased by 30% (P < 0.05). The potential for increasing the performance of junior cross-country skiers seems to be associated with the increased functional capacity of the shoulder girdle muscles.     

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.