Skeletal muscle atrophy can develop under the influence of various factors associated with their disuse, such as immobilization, denervation, or exposure to microgravity. The aim of the study was to conduct a morphological and functional assessment of the soleus, gastrocnemius, and tibialis anterior muscles in models of disuse in rats. The rats were randomly divided into a control group and groups subjected to denervation, tenotomy, and hindlimb unloading (HU). During the experiments, a decrease in muscle fiber diameter was observed in all experimental groups. Tenotomy resulted in a decrease in dystrophin immunoexpression. With HU, the level of dystrophin decreased, but by day 35, recovery was observed in the gastrocnemius and tibialis anterior muscles, while in the soleus muscle, the level continued to fall. After denervation, the dystrophin content also decreased but then increased, reaching control values in the soleus muscle by day 35. The level of neuronal NO synthase decreased significantly in all experimental groups. Denervation and tenotomy lead to pronounced changes in the contractile function of the soleus muscle in rats.

Postural control is a multilevel adaptive system that stabilizes the body in space through dynamic sensory rebalancing and predictive neuromotor regulation. This review synthesizes current data on the neural mechanisms of balance maintenance, individual strategies for integrating multisensory information, and the role of immersive virtual reality as a controlled experimental and neuromodulation platform, synthesising evidence from 73 studies across neuroscience, cognitive psychology, and VR-based rehabilitation. Particular attention is paid to the cognitive style of “field dependence/independence”, which reflects stable preferences for the dominance of visual or vestibular-proprioceptive signals and consistently predicts the selection of postural strategies. We show that traditional averaged models ignore interpersonal variability, whereas immersive VR allows for the parametric induction of sensory conflicts, quantitative assessment of sensory dependence profiles, and facilitates the study of adaptive reorganization at the cortical, brainstem, and spinal levels. The review substantiates the need to move from standardized protocols to personalized approaches in diagnostics and neurorehabilitation that consider individual patterns of input rebalancing. The integration of behavioural metrics with neurophysiological markers in a VR environment provides a foundation for developing predictive balance models and targeted training interventions. However, the translational application of VR-based approaches requires careful consideration of methodological limitations, including cybersickness, hardware latency, and ecological validity, to ensure robust and generalisable outcomes.

Spinal cord injuries must be treated as soon as possible. Studies of NASCIS protocols have questioned the use of methylprednisolone therapy. This study aimed to evaluate the effect of local delivery of methylprednisolone succinate in combination with a tri-block copolymer in rats with spinal cord injury. The experiments were conducted in accordance with the bioethical guidelines. We evaluated the state of the motor centers below the level of injury by assessing the amplitude of evoked motor responses in the hind limb muscles of rats during epidural stimulation. Kinematic analysis was performed to examine the stepping cycle in each rat. Trajectories of foot movements were plotted to determine the range of limb motion, maximum foot lift height, and lateral deviation of the foot in rats on the 21st day after spinal cord injury. We have shown that the local application of methylprednisolone succinate in combination with block copolymer leads to recovery of center excitability by 21 days after injury. In rats, they recovered weight-supported locomotion, directional control of walking, and balance. The proposed assessment method provides valuable information on gait disturbances following injury and can be utilized to evaluate the quality of therapeutic interventions.

Background: The functional state of skeletal muscle is governed by the interaction of mechanical loading, neural control, and proprioceptive afferentation. Nonetheless, the relative impact of the disruption of these components on muscle function and structure remains insufficiently characterized. Methods: In the present study, we investigated three rat models of muscle disuse and two combined models: hindlimb unloading (n = 40), denervation (D, n = 40), tenotomy (T, n = 40), and the combinations HU + D (n = 8) and HU + T (n = 8), with the cumulative effects evaluated at 7, 14, 35, and 50 days. Functional changes were assessed using electrophysiological methods (M-response recording), and structural changes were evaluated by histological, immunohistochemical, and immunofluorescence analysis. Results: The disuse models elicited significantly distinct trajectories of muscle maladaptation. Hindlimb unloading induced coordinated functional and structural remodeling; denervation provoked early functional decline followed by structural changes; tenotomy largely preserved functional activity despite progressive structural remodeling. The combination of denervation with unloading partially attenuated the negative effects, whereas the combination of unloading and tenotomy led to functional enhancement in some cases. These findings provide insight into the degree of convergence, additivity, and synergy of the disruption of regulatory components and indicate that reduced electrical activity is not invariably associated with synchronous structural degradation, revealing a functional–structural dissociation wherein functional status fails to reflect structural integrity. Conclusions: This observation suggests a previously unrecognized mechanism of maladaptation, which diverges from classical atrophy, broadening our understanding of muscle disuse physiology and offering new perspectives for the development of preventive and therapeutic strategies against atrophic processes.

Skeletal muscles are highly dynamic tissues that respond to various stimuli, especially changes in mechanical load. Therefore, active use or disuse directly affects the skeletal muscle phenotype, influencing metabolism, protein expression, and morphological characteristics. In this regard, it is relevant to study the mechanism of the influence of motor activity on the state of skeletal muscles. The aim of this work was to assess the state of skeletal muscles in rats with impaired motor activity. The study was conducted on twenty-five adult nonlinear laboratory mature rats (weight 180–220 g) in compliance with bioethical standards. Animals were divided into groups with denervation («D», n = 5), tenotomy («T», n = 7) and their combinations with hindlimb unloading (HUD, n=5; HUT, n=8). The values of the parameters before surgery served as a control. To study the state of the peripheral part of the neuromuscular apparatus, the maximum amplitude of the motor (M) response of the gastrocnemius, soleus, and tibialis muscles of the hind limbs of a rat was assessed before surgery, on days 7 and 50. Denervation caused a significant decrease in the maximum amplitude of the M-response in all muscles on day 7 (to 7±3 % of the control), which was not restored by day 50. Tenotomy decreased the amplitude in the gastrocnemius and soleus muscles to 46±20 % and 43±15 %, respectively, but increased it in the tibialis muscle (108±10 % of the control). By day 50, the amplitude in the soleus muscle recovered to 68±10 %, and in the tibialis muscle to 120±4 %. In the HU with denervation group, a decrease in the M-response level was observed in the gastrocnemius, soleus, and tibialis muscles by day 7 (to 15±3 %, 18±7 %, and 24±8 %, respectively), with insignificant recovery by day 50. With HU with tenotomy, the amplitude in the gastrocnemius and soleus muscles decreased to 47±6 % and 38±5 %, while in the tibialis muscle it increased to 141±8 %. By day 50, the amplitude in the soleus muscle was restored to 59±10 %. In the tibialis muscle, there is a significant increase in amplitude by day 50 (153±20 %). The results showed that on the 7th day of HU combined with denervation, there was also a deterioration in the condition of the peripheral part of the neuromuscular apparatus in the rat. Tenotomy, transection of the Achilles tendon, as well as the use of denervation, transection of the sciatic nerve, are some of the common methods for studying the role of neuromuscular activity in regulating the functional properties of striated muscle fibers of various functional profiles. During tenotomy, muscle inactivity is observed against the background of loss of afferent (proprioceptive), but preserved efferent innervation, while during denervation, complete deafferentation is observed, which is also expressed in muscle tissue inactivity. A number of observations indicate that the elimination of support afferentation is the main mechanism leading to the «switching off» of the electrical activity of the motor units of the postural muscle under conditions of hindlimb unloading. In our study, changes in the parameters of the M-response of the soleus muscle demonstrated that with a combination of the elimination of support afferentation and proprioceptive afferentation, as well as complete deafferentation, the negative impact of hindlimb unloading is aggravated. Based on the above observations, it can be assumed that the change in muscle properties during hindlimb unloading is caused, among other things, by changes in the neuronal control of the activity of motor units.