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Contractile properties of skeletal muscles of rats were investigated using glycerinated muscle preparations that were obtained from Cosmos-1887 animals flown for 13 days (plus 2 days on the ground) and from rats that remained hypokinetic for 13 days on the ground. In the flow rats, the absolute mass of postural muscles remained unchanged while their relative mass increased; this may be attributed to their enhanced hydration which developed during the first 2 days after landing. Strength losses of the postural muscles were less significant than after previous flights. Comparison of the Cosmos-1887 and hypokinesia control data has shown that even 2-day exposure to 1 G after 13-day flight can modify drastically flight-induced changes.

By computer tomography, mineral density of lumbar vertebrae and their segments as well as back muscle (++ilio-costal, extensor and ++inter-spinal) density and mass were measured in four Salyut-7 crewmembers before and after extended flights (of 5 and 7 months in duration). These findings are in good agreement with the results of prolonged bed rest studies in which trabecular bone of vertebral bodies was investigated: mineral density diminished only in some (approximately 10%) of the test subjects. At the same time mineral density loss was seen in the vertebral elements where muscles were attached. Also, muscle mass was reduced. It is emphasized that the level of changes was not correlated with flight time. Further investigations in this area are discussed.

Nine volunteers, aged 27 to 41 years, were exposed to 370-day head-down tilting during which their tibia bones were examined by measuring acoustic parameters with the aid of exponential point concentrators located at a 15 mm distance. Although the bone acoustic profile showed individual variations, the decrease of the average ultrasound velocity in the middle part and the gradient of the ultrasound velocity in the distal part of the diaphysis occurred primarily in the first half of the bed rest study, thus reflecting changes in bone adaptation to mechanical loads (redistribution of elastic properties along the bone). The acoustic parameters measured noticeably responded to countermeasures used (or not used) during bed rest (exercise) and therefore can help obtain better prognostic information about bone is compared to the data accumulated by means of monophoton absorptiometry (mineral density measurement). This method can be well used for examining long bones in extended space flight.

Mechanical activity of gastrocnemius and plantaris muscles of dogs at different locomotion patterns was analyzed qualitatively and quantitatively by the method of dynamomyography. Quantitative correlations between the strength parameters and electric activity of the muscles were studied. In walking and running the above muscles showed different types of contractions. This may be related to their morphological, anatomical and topographic features. The data obtained can be used to evaluate the state of skeletal muscles in different experimental models of a diminished motor activity.

Contractile properties of glycerinated fibers of skeletal muscles of rats flown for 18.5 days on Cosmos-936 were investigated. In slow antigravitational muscles (soleus m. and triceps brachii m.), decrease in the amplitude of isometric tension and performance as well as acceleration of the contraction development were observed. The studies point to a high specificity of reactions of skeletal muscles to the experimental conditions, depending on their functional specialization. It is suggested that changes in contractile properties of myofibrillar proteins may contribute to the adaptive rearrangement of functional properties of antigravitational muscles under the influence of space flight.

Bone density in different skeletal compartments was measured in 9 healthy volunteers exposed for 370 days to head-down tilting (-5 degrees). Measurements were carried out using noninvasive techniques: quantitative computer tomography and dual photon absorptiometry (mono- and dichromatic). After bed rest no distinct mineral losses were seen in lumbar vertebrae, femoral diaphysis, tibial diaphysis, or forearm bones of most subjects. Mineral density of the femoral neck decreased in most subjects. The results are discussed with special emphasis on comparative values of the noninvasive methods, variations in the parameters under study during bed rest, and effectiveness of various countermeasures employed.

Experiments were carried out to measure time and force parameters of isometric contractions and structural parameters of muscles of hind limbs of rats which were exposed to hypokinesia for 130 days and then were kept under surveillance for 3 months. During recovery certain functions of the contractile system returned to the normal. At the same time M. soleus displayed persistent changes that were indicative of atrophic developments. Unlike M. soleus where delayed contraction (due to an increase in the time of relaxation) was followed by losses in force, fast muscles (M. ext. digit. longus and M. plantaris) showed recovery of force parameters. They also exhibited delayed contraction due to an increase in the time of tension development and half-relaxation. These differences are associated with dissimilar function and structure of muscular fibers. On the whole, the pattern of recovery of the motor functions reflects responses to an increased load of the neuromuscular system of animals which are kept in large cages after prolonged hypokinesia.

Contractile properties of preparations of glycerinated myofibers and subunit composition of myofibrillar proteins of skeletal muscles were studied using rats flown on Kosmos-1514 (pregnant females) and Kosmos-1667 (males). After the 5- and 7-day flights the strength and velocity of contraction of myofibers decreased, although this change was not correlated with functional differentiation of muscles. The myosin population tended to vary in terms of the proportion of fast and slow isoforms. It is concluded that physiological properties of skeletal muscles at an early stage of orbital flights deteriorated primarily due to a decline in the functional activity of the excitation-contraction conjugation system of myofibers.

The effect of 21-day exposure to +2 Gx and +1.1 Gx on the contractile properties of different muscle groups of rat fore- and hindlimbs was examined, using glycerinated myofibers in the ATP + Ca2+ solution. It was found that the isometric contraction strength and velocity increased, the performance of the postural extensors also grew: that of the soleus m. in the +2 Gx rats and that of the triceps brachii m. in the +2 Gx and +1.1 Gx rats. The contractile changes of the flexors of fore- and hindlimbs were insignificant and sometimes oppositely directed. The different responses of the muscles to acceleration were associated with the differences in their function, metabolism and biomechanics.

Results of animal (rat) experiments carried out onboard biosatellites Cosmos-605, 690, 782, 936 and 1129 are presented with emphasis on changes in metabolism and musculo-skeletal system. The modifying effect of weightlessness on the animal radiosensitivity is considered. The use of artificial gravity as a countermeasure against adverse effects of weightlessness is discussed. As an immediate perspective, primate experiments aimed at a detailed study of mechanisms of weightlessness induced changes in the structure and function of the cardiovascular, musculo-skeletal and vestibular systems are described.

Mechanical properties (stress and strain) of bones from rats of different ages exposed to weightlessness, hypodynamia or hypokinesia were examined upon torsion. As compared to the controls, the femur of Cosmos-1129 rats showed high deformability. Also, skeletal bones of young rats proved more sensitive to hypodynamia than those of adult animals.