INTRODUCTION:Dry immersion (DI) is a ground-based model of simulated weightlessness that reduces support and proprioceptive input. This model produces reversible sensorimotor deconditioning and allows simulation of the early acute readaptation phase after spaceflight. We aimed to determine changes in spatiotemporal gait parameters and shin muscle work resulting from 7 d of DI, and whether plantar pressure distribution shifts accompany these changes. METHODS:A total of 28 healthy males (14 DI, 14 controls) completed overground walking tests twice pre-DI and 2-3 h post-DI at first standing. Spatiotemporal parameters and plantar pressure (10 zones) were recorded. Surface electromyography [tibialis anterior, gastrocnemius (caput laterale), soleus] was sampled at 2000 Hz; the root mean square of electromyography was computed over phase-relevant intervals. RESULTS:After DI, walking speed, step frequency, and step length decreased by 19.6%, 8.3%, and 12.3%, respectively. The stance phase increased (≈2% of gait cycle) due to longer double support. Plantar pressure showed posterior-lateral redistribution: reduced loading at the toes and medial forefoot, with increased loading at the heel; lateral forefoot changes showed trends in some subjects. Root mean square electromyography increased in all recorded muscles. DISCUSSION:The results obtained are consistent with previous findings after spaceflight and its ground-based models. At the same time, they extend existing knowledge by adding new data on changes in plantar pressure distribution. These alterations may represent both the consequence and the target of locomotor strategies that compensate for gait instability. These findings clarify locomotor risks after short spaceflights. Saveko A, Bekreneva M, Ponomarev I, Shigueva T, Rukavishnikov I, Tomilovskaya E. Reorganization of human gait and foot pressure patterns after 1-week dry immersion. Aerosp Med Hum Perform. 2026; 97(4):235-242.

To date, there is evidence that support stimulation of the feet in neurological practice is a promising method for motor rehabilitation. The implementation of support stimulation is possible in various ways, but according to the results of modern research, mechanical stimulation of the feet demonstrates the greatest effectiveness. At the same time, the area, localization and intensity of mechanical support stimulation determine the activation features of the cutaneous mechanoreceptors of the soles, affecting evoked motor responses. From this perspective, the question of which type of mechanical support stimulation is the most practical and prospective remains relevant. In this review, we consider the currently existing approaches to mechanical support stimulation, as well as the results of their application in medical practice in order to improve motor abilities in patients.

Walking and running on treadmill BD-2 in the active and passive modes are the core of the Russian countermeasure system on board the International space station (ISS). In the active mode, the belt moves owing to the electric drive and in the passive mode the cosmonaut makes the belt move with the help of leg force. One of the primary goals of this investigation is better understanding of the physiological aspects of these training sessions. Purpose of the investigation is comparative analysis of biomechanical and electromyographic characteristics of walking in long-term space missions (SM) using the BD-2 active and passive modes. The investigation involved 22 cosmonauts at the age of 45.7 ± 4.7 yrs. in the course of 115- to 340-day missions to the ISS. The cosmonauts performed the locomotion test monthly (no less than 4 times). Two sessions of the investigation were conducted prior to launch and two sessions on days 8 and 12 in the period of post-flight recovery. Protocol of the locomotion test (3-min walking) was performed twice, i.e. in the active and passive modes. Walking biomechanics was assessed using the podogram recorded with pressure cells built in sensing insoles. Electromyographic activity of the next four muscles was measured simultaneously: anterior tibial muscle, soleus, lateral gastrocnemius and quadriceps muscle of the thigh. Results demonstrate greater values of support reactions and electromyographic activity of the gravity-dependent soleus m. in the passive mode as compared to the active mode in all test sessions. This can be, probably, explained by a tighter foot contact with the treadmill belt in the passive mode and, as a consequence, increased intensity of support afferentation signals. It is notable that this difference grows in microgravity.

The effectiveness of the support stimulation of the mechanoreceptors of the feet has been first shown in space medicine. In space flight during support withdrawal with non-use of postural muscle, this method is a countermeasure against sensorimotor disorders. Later, it was applied in clinical practice as treatment of motor disorders after stroke, in Parkinson's disease, infantile cerebral palsy, neuropathies, and many others. The impact of such stimulation on motor control is due to spinal and supraspinal mechanisms, which are activated by creating an additional support afferent input through the plantar surface. Many studies confirmed the positive effect of support stimulation on motor control, but the protocols of such stimulation remain the subject of active discussion. This review includes (1) the features of sensitivity of the foot sole cutaneous afferents to the support mechanical stimuli, (2) data on spinal and supraspinal responses of the nervous system to support stimulation, and (3) the results of applying this approach in neurological practice via various techniques. Summarizing this information, the authors highlight the most promising ways and types of medical devices for foot support stimulation in neurology.

Short-radius centrifugation (SRC) is a promising and economically feasible countermeasure in space flight and applies to gravity therapy in terrestrial medicine. The potential occurrence of undesirable orthostatic and vestibular reactions limits the use of this method. One way to minimize these risks is the ability of a human to adapt to the effects of overload. It is known that artificial gravity training may improve orthostatic tolerance. New data demonstrated that cardio-postural interactions and muscle-pump baroreflex activation are present during short-arm centrifugation. Based on previous studies, we hypothesized that repeated SRC in the interval training mode with angular velocities from 22 to 28 rpm may also improve postural tolerance. Six healthy male volunteers were observed before and immediately after five consecutive SRC sessions. The rest between SRC was at least three days. The SRC mode was an interval and included five 300-second platforms with 1.27 g at the feet and four 300-second platforms with 2.06 g at the feet. We registered the main postural characteristics and ground reaction forces data when the participant kept the center of pressure at a given point in a standing position with biofeedback and without this. After the first SRC session, there was a significant posture decondition. The SRC training effect was already noticeable after the second SRC session and was stable until the end of the experiment. The results demonstrate the development of postural tolerance to artificial gravity exposure in this mode and expand the understanding of sensorimotor adaptation capabilities.

In the first days after a spaceflight (SF), re-entry motion sickness and motor coordination problems reflect the need to readapt back to the natural gravitational state. Gravity is a natural stimulus for the receptors of vestibular apparatus, which plays an important role in multisensory interactions. Changes indicating an increase in excitability of the vestibular apparatus during SF (Kornilova et al., 2017) suggest a high probability of the occurrence of gaze-evoked nystagmus after prolonged SF. Russian-American experiment "Field Test" included a nystagmus test. 22 ISS crewmembers (14 Russian cosmonauts and 8 astronauts; flight duration 159.8 +/- 19.5 days) participated in the experiment. The study was conducted twice before flight and several times after flight, starting within 3 h after landing. In a seated position, astronauts tracked with their eyes only (without moving their head) horizontal and vertical movements of the researcher's finger from the central position to the gaze end points (right, left, upper). Eye movements were recorded with a video camera. The videos were analyzed qualitatively for presence of nystagmus. Preflight, gaze-evoked nystagmus was detected in 5 people, the greatest changes were observed on landing day. 10 crewmembers exhibited nystagmus in the extreme left gaze position and 13 crewmembers - in the extreme right gaze position (partial recovery was observed 1-4 days after SF). A noticeable decrease in the frequency of manifestation of the nystagmus was observed only 10-13 days after landing (n = 16). Gaze-evoked nystagmus is usually considered a clinical sign of cerebellar alterations. However, it is often described in healthy people with a prevalence of up to 21 %. In a similar study involving 18 astronauts, participants of long-term SF, the frequency of occurrence of gaze-evoked nystagmus also increased in the first hours after SF (Reschke, Good and Clement, 2017). However, in this study, a detailed analysis of the presence of nystagmus in various directions was conducted for the first time. Of particular interest is the frequent detection of a gaze-evoked nystagmus in the right position after SF- this phenomenon may be a sign of presence of a central vestibular imbalance (Robinson et al., 1984), which also occurs in patients with cerebellar disorders (Bayer and Dietrich, 2011). The results allow us to expand our understanding of the severity and frequency of vestibular disorders and the dynamics of their recovery after prolonged SF.

During interplanetary expeditions, the crew must adapt not only to gravity transitions but also to long-term stay in a limited space of a space station. In such conditions, it develops a significant decrease in motor activity and the formation of a special stereotype of movements in these conditions. Within further planning of ground-based and real interplanetary missions, it is appropriate to assess the impact of these factors on the crew's functional condition, including when modeling lunar gravity using suspension and virtual reality (VR) technologies. The purpose was to determine the functional capabilities of 5 members of the international crew of the 240-day SIRIUS-21 isolation experiment when performing an extravehicular activity (EVA) after 4 and 6 months of isolation in the hermetic facility. During EVA, the crew performed basic motor tasks using VR on an uneven surface: positional tests, voluntary and tandem walking, walking when avoiding and stepping over obstacles, and verticalization from lying and standing on one knee positions. In addition, the EVA scenario included the tasks of controlling the rover while the hands unloading, as well as moving on a sliding surface in a VR environment when the body lunar vertical unloading. In this study, we presented results of qualitative and quantitative analysis of video recording data and qualitative analysis of the electromyographic activity of the muscles of the lower extremities. The results indicate a sufficient level of functional performance of SIRIUS-21 crew members – all the EVA tasks were completed by the crew in full, while no cases of significant loss of balance and signs of pronounced locomotor and vestibular disorders were registered. At the same time, this paper highlights some features of the crew's EVA performance – the effects of sensorimotor training on some tasks with repeated EVA experience, the most common errors, and difficulties in performing the tasks of the EVA scenario.

During space flight, the changes in the functions of the upper limbs can affect the quality of operator activity. At the same time, there are very few data on this topic, because most of the research is focused on the structure and functions of the lower extremities. The aim was to study the characteristics of the grip force control during the decrease of the support and proprioceptive sensory signals in the conditions of the ground-based model of the effects of space flight, Dry Immersion (DI). The duration of DI exposure was 21 days. 10 male volunteers performed tests using a hand dynamometer for maximal voluntary contraction, the maintenance of the reference force, the reproduction of this force from memory, and the grip force gradation test. The subjects performed this series of tests before exposure to DI, then on days 1, 3, 5, 10, 15, and 20 of DI, and days 1 and 3 of the recovery period. The results show that DI exposure led to an increase in proprioceptive sensitivity in the tasks without visual feedback when with open eyes from day 5 of DI the subjects made more mistakes in the reproduction of the reference force using the dominant hand. The sensory processing/modulation disorder under DI factors may cause this phenomenon.

This review includes current and updated information about various ground-based microgravity models and their impact on the human sensorimotor system. All known models of microgravity are imperfect in a simulation of the physiological effects of microgravity but have their advantages and disadvantages. This review points out that understanding the role of gravity in motion control requires consideration of data from different environments and in various contexts. The compiled information can be helpful to researchers to effectively plan experiments using ground-based models of the effects of space flight, depending on the problem posed.

The paper describes the main stages of the protocol and results of a unique 21-day experiment undertaken at the Russian Federation State Research Center Institute of Biomedical Problems of the Russian Academy of Sciences (RAS) (IBMP) under the conditions of Dry Immersion. A cohort of participants consisted of 10 healthy male volunteers (the mean age 29.3 ± 3.56 years). The experiment has demonstrated the feasibility and safety of conducting long-duration immersion exposures, confirming the results obtained during previous shorter exposures, as well as allowed us to describe the dynamics of events during extended chronic stays in the conditions of simulated hypogravity. The accumulated experiences are useful for further research into the efficiency of applying the conditions of simulated microgravity and other prophylactic means as countermeasures against negative effects occurring to human body during extended support and weight unloading.

The aim of the experiment was to evaluate the adaptive responses of biomechanical and electromyographic parameters to vertical unloading (Lunar-0.15 G and Martian-0.35 G) when walking during the 4-month isolation experiment SIRIUS-19 in the ground-based space station model (GBI). The study involved 6 healthy international crew members of the SIRIUS-19 project aged 34 ± 6.2 years (3 women and 3 men). Body Weight Unloading (BWU) conditions was created by the h/p/cosmos airwalk system. The locomotor test included walking (3.5 ± 0.3 km/h) with a sequential change of BWU modes: 5-min walking with 0% BWU (1 G), 5-min walking with 65% BWU (0.35 G) and 5-min walking with 85% BWU (0.15 G). Ground Reaction Force was recorded by the h/p/cosmos treadmill device. Muscle Lab Model 4000e device was used to record the electromyographic signals of the hip and shin muscles. The locomotor test was performed twice before GBI, monthly during GBI and 1 week after leaving isolation. The results obtained before GBI demonstrate that the changes of support and proprioceptive afferentation signals play significant role in reorganizing of the biomechanical structure of motor acts and the development of new movement patterns. The results of the study are consistent with the previously obtained results of other studies in this direction. Despite the fact that during the GBI the participants of the experiment performed regular physical training, a decrease in the performance indicators values was detected, especially pronounced after 100 days of GBI. This is probably due to limited space of a space station model, as well as the development of a special motor stereotype in it. Noteworthy are the results obtained after the 4th session of the experiment, indicating the effect of sensorimotor learning. We think that the data obtained in this study will be useful in research both in gravitational physiology and in clinical medicine.

Skeletal muscle is capable of changing its structural parameters, metabolic rate and functional characteristics within a wide range when adapting to various loading regimens and states of the organism. Prolonged muscle inactivation leads to serious negative consequences that affect the quality of life and work capacity of people. This review examines various conditions that lead to decreased levels of muscle loading and activity and describes the key molecular mechanisms of muscle responses to these conditions. It also details the theoretical foundations of various methods preventing adverse muscle changes caused by decreased motor activity and describes these methods. A number of recent studies presented in this review make it possible to determine the molecular basis of the countermeasure methods used in rehabilitation and space medicine for many years, as well as to identify promising new approaches to rehabilitation and to form a holistic understanding of the mechanisms of gravity force control over the muscular system.

Space technologies greatly contributed not only to space medicine but also to terrestrial medicine, which actively involves these technologies in everyday practice. Based on the existing countermeasures, and due to similarities of sensorimotor alterations provoked by the weightlessness with various neurological disorders, a lot of work has been dedicated to adaptation and introduction of these countermeasures for rehabilitation of patients. Axial loading suit and mechanical stimulation of the soles' support zones are used in mitigation of stroke and traumatic brain injury consequences. They are also applied for rehabilitation of children with cerebral palsy. Complex application of these proprioceptive correction methods in neurorehabilitation programs makes it possible to effectively treat neurological patients with severe motor disturbances and significant brain damage.

This article describes procedures and some results of the first study of females undergoing 3-day Dry Immersion. The experiment “NAIAD-2020” was carried out at the Institute of Biomedical Problems (Moscow, Russia) with the participation of six healthy women volunteers (age 30.17 ± 5.5 years, height 1.66 ± 0.1 m, weight 62.05 ± 8.4 kg, BMI 22.39 ± 2.2 kg/m2) with a natural menstrual cycle. During the study, a standard protocol was used, the same as for men, with a minimum period of time spent outside the immersion bath. Before, during and after Immersion, 22 experiments were carried out aimed at studying the neurophysiological, functional, metabolic and psychophysiological functions of the body, the results of which will be presented in future publications. The total time outside the bath for women did not exceed that for men. Systolic and diastolic pressure did not significantly change during the immersion. In the first 24 h after the end of the immersion, heart rate was significantly higher than the background values [F(4,20) = 14.67; P < 0.0001]. Changes in body temperature and water balance were consistent with the patterns found in men. No significant changes in height and weight were found during immersion. All women reported general discomfort and pain in the abdomen and back. The results of this study did not find significant risks to women’s health and showed the feasibility of using this model of the effects of space flight in women of reproductive age.

16 participants have been subjected to Dry Immersion model (DI) for 5 days. DI reproduces the space flight factors such as lack of support, mechanical and axial unloading, physical inactivity, elimination of vertical vascular gradient. Long-term bed rest is also associated with similar factors, so the results of the study may be useful for clinical medicine. Computer plantography and measuring the stiffness of the soft tissues of the foot and superficial muscles of the shin (mm. tibialis anterior and peroneus longus) were performed twice before DI exposure, on the 2nd and 4th days of DI exposure, as well as on the 2nd day of the recovery period. DI exposure effects the parameters under study in two ways: by raising the longitudinal arch and by flattening the transverse arch, which is accompanied by a decrease in the soft tissues stiffness of the foot and superficial muscles of the shin. The work reveals the phenomenon of compensating the longitudinal arch state by changing the characteristics that reflect the transverse arch state. The results of the study for the first time demonstrate the correlation of the foot morphological characteristics with a decrease in stiffness of mm. peroneus longus and tibialis anterior.

A decrease in muscle tone induced by space flight requires a standardized assessment of changes to control the state of the neuromuscular system. This study is a step toward the development of a unified protocol, aimed at determining the initial effect of the presence or withdrawal of support on muscle tone, the effects of a 2-h supportlessness in Dry Immersion (DI) experiments, and the changes in muscle tone depending on the site of measurement. To perform measurements of changes in muscle tone, we used a MyotonPRO device. The list of muscles that we assessed includes: trunk – mm. deltoideus posterior, trapezius, erector spinae; leg – mm. biceps femoris, rectus femoris, tibialis anterior, soleus, gastrocnemius; foot – m. flexor digitorum brevis, tendo Achillis, aponeurosis plantaris. The study involved 12 healthy volunteers (6 men, 6 women) without musculoskeletal disorders and aged 32.8 ± 1.6 years. At the start of DI, there was a significant decrease in muscle tone of the following muscles: mm. tibialis anterior (−10.9%), soleus (−9.6%), erector spinae (−14.4%), and the tendo Achillis (−15.3%). The decrease continued to intensify over the next 2 h. In contrast, the gastrocnemius muscle demonstrated an increase in muscle tone (+7.5%) 2 h after the start of DI compared to the immediate in-bath baseline. Muscle tone values were found to be site-dependent and varied in different projections of mm. erector spinae and soleus. In previous experiments, we observed a high sensitivity of the myotonometry technique, which was confirmed in this study. To make it possible to compare data from different studies, a standardized protocol for measuring muscle tone for general use in gravitational physiology needs to be developed.