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Impairments in balance control are inevitable following exposure to microgravity. However, the role of particular sensory system in postural disorders at different stages of the exposure to microgravity still remains unknown. We used a method called Dry Immersion (DI), as a ground-based model of microgravity, to elucidate the effects of 6-h of load-related afferent inputs on kinematic characteristics of postural corrective responses evoked by pushes to the chest of different intensities during upright standing. The structure of postural corrective responses was altered following exposure to DI, which was manifested by: (1) an increase of the ankle and knee flexion during perturbations of medium intensity, (2) the lack of the compensatory hip extension, as well as diminished knee and ankle flexion with a further increase of the perturbation intensity to submaximal level. We suggest that the lack of weight-bearing increases the reactivity of the balance control system, whereas the ability to scale the responses proportionally to the perturbation intensity decreases. Disrupted neuromuscular coordination of postural corrective responses following DI can be attributed to adaptive neural modifications on the spinal and cortical levels. The present study provides evidence that even a short-term lack of load-related afferent inputs alters kinematic patterns of postural corrective responses, and can result in decreased balance control. Because vestibular input is not primarily affected during the DI exposure, our results indicate that activity and the state of the load-related afferents play critical roles in balance control following real or simulated microgravity.

The study focused on the effects of duration of a single aerobic exercise session of moderate intensity (60% of {ie296-1}) on the activation of PGC-1α gene expression-regulating signaling kinases and the expression of the genes that regulate mitochondrial biogenesis and play a role in regulating catabolism. Nine athletes ({ie296-2} 59 mL/min/kg) cycled on a ergometer for 30, 60, and 90 min. A exercise-induced increase in PGC-1α gene expression was found to occur without activation of the kinases AMPK, p38 MAPK, and CaMKII. A comparable increase in PGC-1α gene expression was observed after 60- and 90-min exercises, while VEGFA gene expression increased only after 90-min exercise. Even 90-min exercise of the given intensity did not activate the FOXO1-E3 ubiquitin ligase pathway, nor did it increase the expression of catabolism-regulating genes.

Introduction: We investigated the effect of resist- ance exercise intensity and exercise-induced metabolic stress on the activation of anabolic signaling and expression of myo- genic genes in skeletal muscle. Methods: Ten strength-trained athletes performed high-intensity (HI, 74% of 1-repetition maxi- mum (RM)), middle-intensity (MI, 54% 1RM), or middle-intensity (54% 1RM) no-relaxation exercise (MIR). Kinase phosphoryla- tion level and myogenic gene expression in muscle samples were evaluated before, 45 min, 5 h, and 20 h after exercise. Results: The lactate concentration in MI was approximately 2- fold lower than in the 2 other sessions, and was highest in MIR. The phosphorylation level of extracellular kinase 1/2 Thr202/Tyr204 after exercise was related to metabolic stress. Metabolic stress induced a decrease in myostatin mRNA expression, whereas mechano-growth factor mRNA level depended on exercise intensity. Conclusion: This study demonstrates that both inten- sity and exercise-induced metabolic stress can be manipulated to affect muscle anabolic signaling. Muscle Nerve 000:000-000, 2014

The hypertrophic effect of strength training is known to be due to mechanical and metabolic stimuli. During exercises with the restricted blood supply of working muscles, i.e., under the conditions of intensified metabolic stress, the training effect may be achieved with much lower external loads (20% of one repetition maximum). The effects of 8 weeks of high-intensity (80–85% of one repetition maximum) strength training were compared to low-intensity (50% of one repetition maximum) training without relaxation. The high-intensity strength training resulted in higher increases in strength and size of the exercised muscles than training without relaxation. During high-intensity training, at the muscle cross section, an increase in the area occupied by type II fibers prevails; while, during training without relaxation, an increase in the area occupied by type I fibers prevails. An exercise session without relaxation leads to a more pronounced increase in the secretion of the growth hormone, insulin-like growth factor-1, and cortisol. The expression of gene regulating myogenesis (Myostatin) is changed in different ways after a high-intensity strength exercise session and after an exercise session without relaxation. Low-intensity strength training (50% of one repetition maximum) without relaxation is an efficient way for inducing increases of the strength and size of the trained muscles. This low-intensive type of training may be used in rehabilitation medicine, sports, and fitness.

The results of studies of influence of mechanostimulation of the soles’ support zones on the effects of micro-gravity in the motor system are presented. It was shown that mechanostimulation of the soles’ support zones in the regimen of slow and fast walking, every day during 7 days of dry immersion (DI), eliminates fully or suppresses considerably the effects of micro-gravity. Decrease of the force–velocity properties or atrophic changes in the leg extensors were not developed after exposure to simulated micro-gravity in the subjects who “walked” 20 min of each hour six times a day; the transverse stiffness was only slightly lowered and the amplitude of electromyographic activity at rest stayed unchanged. The level of orthostatic deficiency in this group was also lower than in the group without stimulation. These experimental results being in full agreement with previous studies point out to the leading role of the support deafferentation in gravitational deprivation of the tonic muscle system's activity and thus that adequate mechanostimulation of the soles’ support zones can be proposed as a countermeasure against the negative effects of weightlessness.

The paper summarizes the results of experimental studies advocating for the leading role of support afferentation in control of the functional organization of the tonic muscle system. It is shown that transition to supportless conditions is followed by a significant decline of transverse stiffness and maximal voluntary force of postural (extensor) muscles limiting their participation in locomotion and increasing involvement of phasic muscles. Mechanical stimulation of the support zones of the soles under the supportless conditions eliminates all the above-mentioned effects, including changes in transverse stiffness and maximal voluntary forces of postural muscles, and consequent loss of influence of postural muscles in the locomotor activity. It is suggested that support afferentation, facilitating (support is present) or suppressing (support is absent) the tonic motor units (MUs) activities, defines the coordination patterns of postural synergies, and ensures the optimal strategy of corrective postural responses.

The results of studies of the effects of mechanostimulation of the soles’ support zones on the effects of microgravity in the motor system are presented. It was shown that mechanostimulation of the soles support zones in regimen of slow and fast walking, being used daily during 7 days dry immersion, eliminates fully or suppress considerably all the microgravity effects. In subjects in which stimulation was applied six times a day by 20 min every hour the decrease of force–velocities properties and atrophic changes in the leg extensors after the exposure to microgravity were not revealed. Their transverse stiffness was only slightly lowered and the amplitude of electromyographic activity at rest stayed unchanged. The level of orthostatic deficiency in this group was also lower than in the group without stimulation. Thus presented experimental results in full agreement with previous studies allow to conclude that support afferentation plays the leading role in gravitational deprivation of the activity of tonic muscle system and that adequate mechanostimulation of the soles support zones can be used as a countermeasures mean in weightlessness.

The aim of the present study was to investigate the effect of acute aerobic exercise on the expression of PGC-1α transcript variants in human skeletal muscle. Seven endurance-trained athletes performed a 90-min cycling test (62% of VO2max). At resting state, the levels of N-truncated (NT)-PGC-1α and PGC-1α exon 1a-derived transcripts were significantly higher (20-fold; P0.05) than those of PGC-1α exon 1b- and 1c-derived transcripts. Acute exercise did not change the PGC-1α exon 1a-derived expression level, but it did increase the expression level of NT-PGC-1α mRNAs 6-fold, and the expression levels of PGC-1α exon 1b- and 1c-derived mRNAs200-fold (P0.05). We conclude that NT-PGC-1α transcript expression in resting muscle and after acute moderate-intensity exercise constituted a significant share of total PGC-1α expression. The exercise led to a higher level of PGC-1α expression from alternative promoters (exon 1b- and 1c-derived mRNA) than from the canonical proximal promoter (exon 1a-derived mRNA).