Long-term dry immersion: review and prospects

Dry immersion, which is a ground-based model of prolonged conditions of microgravity, is widely used in Russia but is less well known elsewhere. Dry immersion involves immersing the subject in thermoneutral water covered with an elastic waterproof fabric. As a result, the immersed subject, who is freely suspended in the water mass, remains dry. For a relatively short duration, the model can faithfully reproduce most physiological effects of actual microgravity, including centralization of body fluids, support unloading, and hypokinesia. Unlike bed rest, dry immersion provides a unique opportunity to study the physiological effects of the lack of a supporting structure for the body (a phenomenon we call \u27supportlessness\u27). In this review, we attempt to provide a detailed description of dry immersion. The main sections of the paper discuss the changes induced by long-term dry immersion in the neuromuscular and sensorimotor systems, fluid-electrolyte regulation, the cardiovascular system, metabolism, blood and immunity, respiration, and thermoregulation. The long-term effects of dry immersion are compared with those of bed rest and actual space flight. The actual and potential uses of dry immersion are discussed in the context of fundamental studies and applications for medical support during space flight and terrestrial health care

Locomotion with a supplementary motor task after the exposure to 21-day dry immersion

The paper presents the results of studying changes in human locomotion biomechanics following the 21-day exposure to dry immersion. Participants were 8 normal male subjects at the age of 45.3 ± 5.4 years who were tested twice on days 14 and 7 before DI and immediately after its completion. After 21 days in immersion, significant changes in the clearance between the foot and bar in the range from 5 to 30 cm were observed only when the obstacle was 30 cm high. It is noteworthy that step length also reduced during crossing lower obstacles. Therefore, after DI we observed changes in two motor task parameters (stepping over an obstacle), i.e. widening of the clearance between the foot and bar, and decrease of the step length. © 2020 Slovo Ltd. All rights reserved

Dynamics of Body Composition Indices and Biochemical Parameters in Participants of Countermeasure-Free 21-Day “Dry” Immersion

Abstract: Time-dependent changes in body composition and the levels of hormones involved in regulating energy metabolism and eating behavior were studied in ten healthy volunteers who were exposed to dry immersion (DI) for 21 days without the use of countermeasures to prevent the negative effects of the experimental conditions. Bioimpedance analysis (BIA) was used to assess the body composition in the test subjects. The proportion of lean mass decreased, while the fat component increased in the subjects under the influence of factors of 21-day DI. Cluster analysis isolated two equal homogeneous groups of subjects with a reduced group variability of the parameters of body composition and systemic regulation of energy metabolism. A significant decrease (p < 0.05) in relative skeletal muscle mass (SMM%) was observed after 21-day DI in the group with a higher relative body fat mass (FM), a lower relative fat-free mass (FFM), and a higher basal metabolic rate. SMM was stable, while SMM% increased (p < 0.05) after 21-day DI in the group with a lower relative FM, a higher FFM, and a lower basal metabolic rate. A significant increase in blood insulin was observed during DI in this group. Leptin and triglyceride concentrations differed between the groups in different periods of the experiment. © 2021, Pleiades Publishing, Inc

NEUROMUSCULAR AND MYOTENDINOUS ALTERATIONS IN-FLIGHT IN PLANTAR FLEXOR MUSCLES

BACKGROUND Despite extensive exercise countermeasures, astronauts still experience sizable deficits in calf muscle mass and strength. Recent muscle biopsy data suggest deficits are associated with metabolic deviations [1]. Many studies have tested astronaut strength before and after spaceflight. The one study that tested in-flight reported a significant reduction in isometric and isokinetic knee extensor strength that was pronounced from the very beginning of the space sojourn [2]. This is in stark contrast to bed rest studies, where a gradual and continuous loss of muscle mass and strength has been repeatedly reported. METHODS The Sarcolab3 study attempted to describe the time course of changes in isometric and isokinetic muscle strength and in muscle mass. Crew members were tested on board the ISS after 8.9 (SD 3.0), 49.1 (10.1) and 131.5 (SD 27.7) days in-flight, as well as pre-and post-flight, using the Muscle Atrophy Research and Exercise System (MARES). Specifically, maximal voluntary torques in plantar flexion and knee extension were measured at various angles in order to establish the torque-angle relationship. Simultaneously, activation capacity was assessed by supra-maximal myo-electrical stimulation superimposed to a maximum voluntary contraction. Calf muscle volume was assessed by magnetic resonance imaging pre-and post-flight. RESULTS Results demonstrate early declines in muscle strength at flight days 9 and 49, and a tendency for the decaying time course to level off at flight day 131. Activation capacity of plantar flexor, as elicited by myo-electrical stimulation, was maintained during in-flight and post-flight testing. At 4 days post-flight, soleus muscle volume had declined by 15-20% as compared to pre-flight. CONCLUSIONS Results suggest that existing exercise countermeasures are still not fully effective for preventing weakness and wasting of the calf musculature. The observed time course of in-flight muscle loss seems more compatible with results from bed rest. Potentially, the rate of muscle wasting may decline during the second half of 6-month missions with the current countermeasure exercise regimens. REFERENCES 1. Rittweger, J., et al., Sarcolab pilot study into skeletal muscle's adaptation to long-term spaceflight. NPJ Microgravity, 2018. 4: p. 18. 2. Tschan, H., et al., Resistance training - a strategy proposed to coutneract muscular deconditioning in microgravity, in 10 Years Space Biomedical Research and Development in Austria, H. Hinghofer-Szalkay, Editor. 2001, Facultas: Wien. p. 95-108