The paper considers the process of interaction of individual muscles and muscle groups serving various joints of the body in order to minimize vertical stability disorders caused by respiratory movements of the chest. The most significant control variables in the process of regulation of intermuscular interaction in order to maintain the stability of the vertical position of the body are considered. The analysis was performed using factorization of muscle electrical activity data, values of articular angles and movements of body segments. It was found that the strategy of maintaining a vertical stance is associated with the control of the hip and neck segments, and with an increase in the disturbing effect, other segments of the body are involved in synergy. An increase in the depth of breathing is accompanied by the inclusion of previously unused muscle modules and a change in the degree of involvement of each muscle in the process of regulating the vertical posture. Such inclusion is reflected in the temporal pattern of activation of synergies at the muscular level, which manifests itself in the formation of additional activation peaks in individual phases of the respiratory cycle. In the process of maintaining vertical stability, muscle activity is moderately associated with the regulation of the position of the general center of mass and is more directed at the formation of kinematic synergies, including changes in the values of a number of articular angles and simultaneous movement of most body segments. The latter, in turn, stabilize variables important for maintaining equilibrium, and synergetic control at the kinematic level increases as the depth of breathing increases.

The article presents an analysis of the muscle synergies involved in making ball throws in different directions and from different starting positions. The study involved 6 highly qualified athletes engaged in rhythmic gymnastics. Electromyograms of the superficial muscles of the upper extremities and trunk were recorded synchronously during the movements, as well as video capture of the movements of body segments. Synergy parameters were extracted from the recorded signals using factor analysis using the principal component method. It has been established that individuals who have mastered a complex motor skill can demonstrate similar motor control strategies. This is manifested in the structuring of intermuscular interaction in the form of two general modules, the degree of involvement of muscles in which is highly similar in the implementation of different motor tasks. The first muscle module implements active movement of the upper limb by jointly activating the muscles of the forearm, shoulder and upper shoulder girdle, and also provides stabilization of the position of the trunk by synchronizing the activity of the muscles of the back and abdomen. The second muscle module is specific and is mainly associated with high involvement in the synergy of the muscles of the upper shoulder girdle and forearm for the implementation of exercises performed without visual control, or from starting positions that limit the mobility of certain parts of the body. Thus, the solution to the problem of coordination of many elements of the motor system may consist not only in reducing the number of executive organs—muscles involved in control, but also in organizing control variables in the form of modules at the kinematic level and their stabilization through muscle synergies.

The study considers the synergetic effects manifested at thelevel of interaction between the various parts of the musculoskeletalsystem with the patterns of bioelectrical activity of skeletal muscleswithin the framework of the concept of hierarchical, modular principleof control. Motor synergies were studied at the muscular, kinematic,and neuronal levels. The spatial and temporal structure of motorsynergies during the performance of a short straight punch by highlyskilled boxers was considered. Synergies were extracted using factoranalysis by principal component extraction. It was found that themuscles that form the spatial structure of the first synergy have patternsof impulse activity of the control signals characteristic of thesynergy. The spatial-temporal characteristics of the movements ofthe body segments, as well as the parameters of the electrical activityof the skeletal muscles in the structure of synergies, demonstratehigh stability in repeated realizations of the motor action andlow variability in the intra- and interindividual comparison. Theintermuscular interaction characteristic of synergy can be achievedby different strategies for organizing the impulse activity of motorunits. A movement that is complex in coordination can have differenttemporal patterns of synergy activation, but the patterns of oneform can be shifted in time relative to each other when they arecompared during multiple realizations of a model movement.

The study showed the sambo wrestlers’ muscle synergies’ spatial-temporal structure, extracted using the PCA method. We considered the individual periods of the "leg grabbing" throw coordination structure. It was revealed the electrical activity of extensive synergies changes depending on registered muscular efforts values, typical for different periods of the performed movement. The synergetic effects of skeletal muscle interaction demonstrate plasticity, manifested in typical patterns of spatial and temporal activation of revealed muscle synergies, which ensures reliable control of motor function in various periods of complex movement coordination performing. Key words: muscle synergies; synergetic effects; intermuscular coordination; motion control, skeletal muscle.

In addition to the traditional determination of hardness and elastic moduli from continuous diagrams of instrumental indentation, it is proposed to determine the yield stress, the characteristic of plasticity, the characteristic relative size of the elastoplastic zone under the indenter, and the volumetric deformation of the material in the area of contact of the indenter with the sample. The indentation diagram shows the transition point to the unconstrained material flow under the indenter. Keywords: indentation, hardness, elastic moduli, contact stiffness, elastic-plastic strains.

A novel approach was designed to regulate the stepping movements in human by means of noninvasive electrical transcutaneous spinal cord stimulation (TSCS) to activate the flexor/extensor motor pools of the lower limbs in the gait cycle. Selective stimulation was delivered automatically based on signals from gyroscope sensors, which served to detect the stance and swing phases. The initiation of hip extension was a trigger for stimulating extensor pools (L1) during the stance phase, and the initiation of hip flexion was a trigger for stimulating flexor motor pools (T11) during the swing phase. In healthy subjects ( n = 6) walking on a treadmill, stimulation at L1 with a frequency of 15 Hz decreased the duration of stance phase by 4% ( p = 0.0457), increased the amplitude of movements in the hip joint by 11% ( p = 0.0266), decreased the movement amplitude in the ankle joint by 17% ( p = 0.0081), and increased EMG activities of the extensors vastus lateralis (VL) (by 31%, p = 0.0441) and gastrocnemius medialis (GM) (by 17%, p = 0.0465) and flexors biceps femoris (BF) (by 26%, p = 0.4637) and tibialis anterior (TA) (by 21%, p = 0.0215) relative to walking without stimulation. Stimulation at Т11 with a frequency of 30 Hz reduced the stance phase duration by 3% ( p = 0.0318) and increased the amplitude of movements in the hip joint by 12% ( p = 0.0467), the knee lifting by 25% ( p = 0.0001), and the terminal anthropometric point height above the surface of support by 19% ( p = 0.0001). The changes were accompanied by increases in muscle activities of the flexors BF (by 18%, p = 0.230) and TA (by 14%, p = 0.0170). The reciprocity coefficient decreased in thigh muscles by 15% ( p = 0.0301) and increased in shin muscles by 5% ( p = 0.0452). Alternating spatiotemporal stimulation at L1 and T11 did not significantly change the durations of the gait cycle and its phases, but changed the kinematic characteristics of movements. The amplitude of movements in the hip joint increased in the stance phase. In the swing phase, higher values were observed for the amplitude of movements in the hip joint, the knee lifting, and the terminal anthropometric point height above the surface of support. EMG activities of thigh and shin muscles increased during stimulation at L1 + T11. EMG activity of extensors was higher than that of flexors in the stance phase, while flexor EMG activity exceeded extensor activity in the swing phase. Thus, the data obtained show the possibility of TSCS selectively to activate the motor pools of the lower extremities, and control their activity to regulate the phases of the stepping cycle during human locomotion.

The improvement of Johnson's model (Johnson (1970), (1985)) takes into account the additional pressure and shear stresses jump at the boundary with the hydrostatic core where it is formed from the material of the elastic-plastic zone. This causes additional volumetric deformations and additional pressure in the core that increases the magnitude of the constant in the Tabor ratio. The effects of the proposed improvement of the Johnson model: additional volumetric deformations and pressure in the core, changes in the Tabor constant and related values of yield strength as well as characteristic size of the elastic-plastic region, were determined on a wide class of materials with different elastic-plastic properties. An analysis of the concept of characteristic (representative) strain is given for these materials.

We studied the regulatory mechanisms underlying isometric and concentric muscle contractions in athletes adapted to stereotypical and situational motor activities. It has been found that the total electromyography (EMG) amplitude of the studied muscles in basketball players during isometric and concentric contractions to voluntary failure in the final period (phase) of contractions decreases, as compared with the initial phase, while the EMG amplitude in short- and long-distance runners was more stable throughout the whole contraction duration. This EMG dynamics was accompanied by certain changes in the amplitude and frequency of EMG turns, confirming that electrical activity in the motor units of muscles is differently organized in basketball players and runners. The coordination structure of the performed isometric and concentric contractions is probably determined by the specificity of the motor program pool formed in athletes during their adaptation to different types of training.

A new analytical model is proposed for penetration resistance of brittle materials that takes into account strain hardening of solid phase of powder material in Mescal zone ahead of penetrator. The strengthening is taken into account by analogy with theories of deformation and compaction of powder materials with elastic-plastic solid phase. The model is an extension of the penetration resistance model proposed by authors earlier. Model performance is demonstrated by example calculation of penetration resistance for glass which at high pressures shows residual densification and increase of elastic modulus. Strain hardening of solid phase was shown to increase penetration resistance.

This paper investigates resistance to hypervelocity penetration of one new ceramic composite of B4C-CaB6 system with significantly improved strength characteristics and its correlation to hardness measurements and structure state. Tendency to breakage and fragmentation of CaB6 in a contact loading zone under indenter facilitates formation of a core from fractured and powdered material, the densification of which during penetration leads to high penetration work and high resistance against penetration. Penetration resistance for each from 3 selected ceramic compositions and different B4C ceramic with porosity up to 30% were calculated and used for a direct analysis of influence of the basic properties of a composite on the penetration resistance. Different components of penetration resistance were estimated and compared for compositions with different mechanical properties and structure. The analysis of influence of free carbon in B4C-CaB6 system on formation of its properties was performed in relation to its hardness and penetration resistance. Sintered ceramic has extremely high macrohardness (HVP=200N, 300N ~ 25GPa) and, correspondingly, resistance to hypervelocity penetration, and is promising for application as an armour material.

A new numerical-analytical model of penetration of projectiles with eroding jacket and elastically deformable (or rigid) projectile central part into infinite targets is developed. Model predicts the influence of main structural parameters of the coating and central core on penetration. Ballistic equations include two modes of motion: joint motion of projectile's core and solid part of its jacket; separate motion of a core and solid part of projectile jacket. Condition of transition from the first mode to the second based on force balance has been determined. From this condition critical velocity and transition time (when motion of a jacket relative to the core begins) are found.

Penetration of glass is strongly influenced by damage. In this work damage is equated to porosity, and strength and moduli are expressed as functions of porosity using well-established relationships. The penetration resistance of porous (damaged) glass is determined and analyzed. Three components of its resistance were separated and conditionally named as dynamic, kinematics and static. Because static component is the one most sensitive to mechanical properties of intact (nonporous) glass and its initial porosity (or damage, if porosity is considered as a damage parameter), the main attention was paid to this component. Its analytic modeling was based on the use for fractured (crushed) glass ahead of a projectile of rheology of porous and powder compactable materials.

We examine the possibility for activation of the involuntary locomotion of the lower limbs by spinal electromagnetic stimulation (ES). The subject laid on the left side. The legs are supported in a gravity-neutral position by special mounting that to provide horizontal rotation in the hip, knee and ankle. ES (3 Hz and 1.56 Tesla) at the T11,-T12 vertebrae induced involuntary locomotor-like movements in the legs. The latency from the initiation of ES to the first EMG burst compoused 0.68 +/- 1.0 s and it shortened at increasing of the frequency ES from 3 Hz to 20 Hz. Thus, the spinal ES can unduce the activation of the locomotor movements in human.

We examined the possibility of initiation of involuntary stepping movements by spinal electromagnetic stimulation (SEMS) during leg suspension. The subject’s legs were supported by a special apparatus in a gravity neutral position that to provide horizontal rotation in the hip, knee and ankle. SEMS (3 Hz and 1.56 Tesla) over the T11–T12 vertebrae induced involuntary locomotor_like movements in the legs. The latency period from the initiation of stimulation to the first EMG burst was 0.68 1.0 s. Increasing the frequency of SEMS from 3 Hz to 20 Hz resulted in shortening of the latency period. Thus, SEMS is able to initiate involuntary stepping in humans.

In this paper, the concepts of mechanics of porous and powder media are applied for development of new analytical model of expansion of spherical cavity in porous brittle materials (ceramics). The model is based on the approach that recognizes the existence of three regions with different rheology: region of comminuted and compacted material; region of pore formation formed by radial cracks; elastically deformed region. Strain-stress state in each region is determined and analyzed. Condition of absence of pore formation region is specified. Cavity expansion pressure is determined. Energy losses on elastic deformation, fracture and compaction (non-elastic deformation) of material are calculated and compared for a number of materials. Penetration depth and target resistance depending on porosity is determined.

Mechanical properties of ZrB2–SiC and ZrB2–ZrSi2–SiC ceramics in the temperature range from 20 to 1400°C were studied. It was found that the introduction of zirconium silicide resulted in pore-free ceramics having bending strengths of 400–500MPa over a wide range of boride–carbide compositions. Zirconium silicide additive did not lead to significant strength and hardness changes at low temperature, but essentially increased Weibull modulus, and, therefore, the reliability of the ceramics. However, zirconium silicide additions resulted in noticeably reduced bending strength in ZrB2–SiC based composites at 1400°C.