Effect of mechanical stimulation of the support zones of soles on the muscle stiffness in 7-day dry immersion

Stiffness of m. soleus (Sol.) and m. tibialis anterior (TA) was evaluated in 16 volunteers during exposure to 7-days dry immersion alone and to the combination of immersion and mechanic stimulation of foot support zones. It was shown that Sol. stiffness decreased progressively starting from day-1 of immersion, whereas TA stiffness, on the contrary, made a sharp rise. Mechanic stimulation of foot support zones slowed down the rate and extent of changes in both muscles.     

Effect of dry immersion in combination with stimulation of foot support zones upon muscle force-velocity characteristics

The complex of motor disturbances arising under conditions of real and simulated microgravity that include decrease of contractile characteristics of postural muscles is likely to be a result of withdrawal of support stimuli. Artificial stimulation of support zones of feet is shown to diminish partially or prevent completely the negative effects of microgravity on the motor system. The aim of the study was to evaluate and compare the changes of contractile properties of extensors and flexors of knee joint measured in isokinetic and isotonic regimes under conditions of simulated microgravity (7 days dry immersion).     

The effects of pH on force and stiffness development in mouse muscles

Changes in force and stiffness during contractions of mouse extensor digitorum longus and soleus muscles were measured over a range of extracellular pH from 6.4 to 7.4. Muscle stiffness was measured using small amplitude (less than 0.1% of muscle length), high frequency (1.5 kHz) oscillations in length. Twitch force was not significantly affected by changes in pH, but the peak force during repetitive stimulation (2, 3, and 20 pulses) was decreased significantly as the pH was reduced. Changes in muscle stiffness with pH were in the same direction, but smaller in extent. If the number of attached cross-bridges in the muscle can be determined from the measurement of small amplitude, high frequency muscle stiffness, then these findings suggest that (a) the number of cross-bridges between thick and thin filaments declines in low pH and (b) the average force per cross-bridge also declines in low pH. The decline in force per cross-bridge could arise from a reduction in the ability of cross-bridges to generate force during their state of active force production and (or) in an increased percentage of bonds in a low force, "rigor" state.     

Function of alpha-motoneurons of the human foot muscles in normal conditions and with descending and segmental deprivation

The characteristics of the central response of the abductor hallucis muscle to stimulation of the posterior tibial nerve were studied in healthy subjects and neurological patients. In normal subjects over 22–23 years old the response has the usual properties of a late potential recorded from the small muscles of the foot (F-wave) whereas in children and adolescents it has the features of the central response of a leg muscle. A unilateral lesion of the posterior sacral roots leads to an increase in amplitude and regularity of the F-wave of the foot muscle on the side of the lesion. This is evidence of the antidromic origin of the principle component of the F-wave and points to increased antidromic excitability of the spinal motoneurons in man in the presence of partial segmental deafferentation. A disturbance of descending control, resulting in the loss predominantly of pyramidal influences, is accompanied by regeneration of the characteristic features of the late potential found in responses recorded in adolescent subjects. The same phenomenon can also be observed in pathology of the posterior horns of the cervical portion of the spinal cord when no pyramidal disorders can be detected clinically. The central response is much less frequently changed in lesions of the ventral structures of higher segments. The significance of descending control for establishment of the level of excitability in the population of motoneurons innervating the muscles of the human foot is discussed.O. V. Kuusinen Petrozavodsk State University. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 563–570, November–December, 1973.     

Effect of vibratory stimulation of foot support areas in rats on the functional state of leg muscles and the content of N2A titin isoforms in gravity relief

In this work, we studied the effect of vibratory stimulation of the foot support zones on the functional state of the leg muscles and the content of N2A titin isoforms in rats under simulated microgravity (suspension model). The results of this study showed that vibratory stimulation of the support zones of the rat foot in a gravity discharge may reduce the drop in the amplitude of leg muscle motor response and undesirable reduction of the titin content.     

Disruptive effects of lateral hypothalamic stimulation on the lick-interrupt cycle in rats

Consummatory licking at a water spout was compared with licking at a dry spout maintained by electrical hypothalamic stimulation in the same rats. Both forms of licking, recorded photoelectrically, were maintained on a fixed ratio 8 schedule. Duration of reinforcement delivery was equated [300 ms]. A computer analysis of the temporal distribution of licks in each 1024 ms period from onset of reinforcement revealed that lateral hypothalamic stimulation decreased the occurrence of licking and disrupted the normally synchronous pattern of this behaviour. An analysis of the effects of delivering lateral hypothalamic stimulation contingent on water-maintained licking revealed that this effect of stimulation was clearly current-dependent. It is proposed that differences in licking rates maintained by water and by electrical hypothalamic stimulation, respectively, are due to response interference in the latter case. This interference effect is also proposed to be a major factor underlying higher reward thresholds for self-stimulation when licking is the operant response.     

The architecture and contraction time of intrinsic foot muscles

Although critical for effective human locomotion and posture, little data exists regarding the segmentation, architecture and contraction time of the human intrinsic foot muscles. To address this issue, the Abductor Hallucis (AH), Abductor Digiti Minimi (ADM), Flexor Digitorum Brevis (FDB) and Extensor Digitorum Brevis (EDB) were investigated utilizing a cadaveric dissection and a non-invasive whole muscle mechanomyographic (wMMG) technique. The segmental structure and architecture of formaldehyde-fixed foot specimens were determined in nine cadavers aged 60–80 years. The wMMG technique was used to determine the contraction time (Tc) of individual muscle segments, within each intrinsic foot muscle, in 12 volunteers of both genders aged between 19 and 24 years.While the pattern of segmentation and segmental –architecture (e.g. fibre length) and –Tc of individual muscle segments within the same muscle were similar, they varied between muscles. Also, the average whole muscle Tc of FDB was significantly (p < 0.05) shorter (faster) (Tc = 58 ms) than in all other foot muscles investigated (ADM Tc = 72 ms, EDB Tc = 72 ms and ABH Tc = 69 ms). The results suggest that the architecture and contraction time of the FDB reflect its unique direct contribution, through toe flexion, to postural stability and the rapid development of ground reaction forces during forceful activities such as running and jumping.     

Activation of the sensorimotor cortex using a device for mechanical stimulation of the plantar support zones

Numerous studies on the mechanisms of the motor control carried out in the interests of space medicine resulted in a concept on the leading role of the support afferent input in the regulation of the postural tonic system in mammals. The implementation of functional magnetic resonance imaging (fMRI) has permitted in vivo brain mapping during stimulation of the support afferent input. The goal of this study was to identify activated regions in the brain during mechanical stimulation of the plantar support zones in different modes using a special Korvit simulator. Twelve healthy volunteers (six women and six men) aged from 22 to 42 years were studied using fMRI, each of them was scanned once. The fMRI protocol for each subject consisted of two different blocked paradigms: (1) with the soles of a subject stimulated in an imitated standing mode and (2) with the soles stimulated in an imitation slow-walking mode. The patterns of activation in each mode were analyzed using the SPM5 statistical software package for each subject and for the group as a whole. All the paradigms showed significant activation (p _correct < 0. 05 at the cluster level) in the primary somatosensory, premotor, dorsolateral and prefrontal cortices, as well as in the insula. The involvement of the prefrontal cortex during simulation of standing and a broad involvement of the primary and secondary sensorimotor cortices during simulation of slow walking were found.     

Effect of stimulating the medial and lateral zones of the respiratory center on the electrical activity of the diaphragm, intercostal muscles and phrenic neurons

Experiments on cats showed that the nucleus of the solitary tract displayed zones whose stimulation provoked separately stimulation or inhibition of the electrical activity of the phrenic neurons and the diaphragm. Stimulation in the nucleus ambiguus of such zones caused stimulation and inhibition of electrical activity of the intercostal inspiratory muscles. In stimulation of the corresponding zone in the giant cell nucleus the electrical activity of both groups of the inspiratory muscles proved to change. It is suggested that the action of stimulation of the giant cell nucleus zones on both groups of inspiratory muscles is mediated through the neurons of the solitary tract and the nucleus ambiguus.     

Effects of anabolics on the thermostimulated current spectrum in calf muscles

The effects of growth substances (zeranol, trenbolone) on calf muscle (pectoralis transversus) have been studied with a recent physical method (thermostimulated current spectroscopy). This method appears promising for detecting meat from calves treated with such hormonal substances. The authors have hypothesized that the observed differences are related to protein modification, the nature of which is yet unknown. A complementary work is now in progress.     

Mechanical stimulation of the support zones of soles: The method of noninvasive activation of the stepping movement generators in humans

The effects of mechanical stimulation of the soles’ support zones in the modes of slow and fast walking (75 and 120 steps per minute) were studied using the model of supportlessness (legs suspension). 20 healthy subjects participated in the study. EMG activity of hip and shin muscles was recorded. Kinematics of leg movements was assessed with the use of videoanalysis system. In 80% of cases support stimulation was followed by leg movements, in 69% of which they had characteristics of locomotions being accompanied by the burst-like electromyographic activities. The order of involvement of leg muscles and organization of antagonistic muscles activities were analogous to those of voluntary walking. The latencies of electromyographic activity in hip and shin muscles composed 5.17 ± 1.08 and 14.01 ± 2.82 s, respectively, the frequencies of bursts differed significantly depending on stimulation frequency. In 31% of cases the electromyographical activity following the stimulation of the soles’ support zones had not burst-like but uninterrupted pattern. Its amplitude rose smoothly reaching a certain level that was subsequently maintained. Results of the study showed that soles’ support zones stimulation in the mode of locomotion could activate a locomotor generator provoking the appearance of locomotion-like activity and that effect evoked by this stimulation includes not only rhythmical but also non-rhythmical (probably postural) components of walking.     

The timing of the electromyogram in the lateral myotomes of mackerel and saithe at different swimming speeds

Electromyogram (EMG) signals from two points at about 40% L and 65% L ( L = length) in the left latera1 muscle of mackerel ( Scomber scombrus L.) L = 28–33 cm a nd saithe ( Pollachius virens L.) L = 42–50 cm were recorded synchronously with films of steady straight swimming motions. In both species, the duration of EMG activity at both electrodes, remains a constant proportion of the tail cycle period Tat all the tail beat frequencies between 1–8 and 13 Hz. In mackerel and saithe respectively: onset of EMG activity at the front was 74% T and 77% T before the left-most tail blade position and fronl EMG-onset occurred 15% T and 18% T before rear onset. The duration of the EMG burst is longer at the front position (41% T and 47% T ) than at the rear (25% T and 27% T ), At all swimming speeds the wave of electrical activation of the muscle travelled between the two electrodes 25% L apart at a velocity between 1.5 and 1.6 L T ⁻¹. Frequencies of spikes within the burst of EMG activity rose from 30–40 Hz at 2 T s⁻¹ to 50–80 Hz at 8 T s⁻¹. In muscle at 40%L EMG-onset happens at phase 30° just after muscle strain at this point reaches its resting length while lengthening (360°). At 65% L EMG-onset occurs earlier in the strain cycle-350° just before the muscle reaches it resting length while lengthening (360°). This could represent within the length of the fish, a phase shift of up to 90° in the EMG-onset in relation to the muscle strain cycle. These timings are discussed in relation to optimized work output and a single instant of maximum bending moment all along the left side of the body.     

RNA concentration in neuron-neuroglia systems of the retina and visual zones of the cerebral cortex during light deprivation and light stimulation]

A two-wave-length cytophotometry of the gallocyanin-chromium alum-stained preparations showed that in adult rats kept for 30 days in complete darkness there was a decrease in the RNA content in the perineuronal neuroglia of the retinal ganglion cell layer only, with no changes in the corresponding neurons. No changes were found in the neurons and in the perineuronal glia of the layer II---III of the visual cerebral cortex. After the end of light deprivation a 2-hour stimulation with a constant or flickering light did not influence the RNA content in the neurons of both regions of the visual analyzer studied, whereas in control rats this stimulation induced a marked increase in the RNA content in these neurons. Qualitative changes in the metabolism of the cellular RNA in the nervous system of adult animals under the effect of light deprivation are emphasized. Differences in the biochemical peculiarities of various neuron-neuroglia systems, depending on their localization in the visual analyzer, are discussed.     

Respiratory effects of stimulation of intercostal muscles and saphenous nerve in kittens

Effects of intercostal muscle stimulation were studied in 2- to 7-day-old kittens under ketamine-acepromazine anesthesia. Animals were vagotomized, paralyzed, and artificially ventilated. Stimuli applied during inspiration (TI) inhibited this phase. Stimulus strength necessary for TI inhibition decreased with time. However, an all-or-nothing effect was not always observed. Stimulation during expiration (TE) prolonged this phase. The responsiveness increased with increasing stimulus delay. The effects of intercostal muscle stimulation were compared with those recorded during saphenous nerve stimulation. Stimulation during TI prolonged this phase. Phrenic activity increased after a short-lasting decrease in the on-going activity. Stimulation during the first 50% of TE had variable effects, whereas stimulation with longer delay shortened this phase. Our results indicated that the pattern of breathing in newborns can be affected by both intercostal muscle and other somatic efferents. However, the mechanisms controlling respiratory timing may differ in newborns and in adults. Different effects of respiratory muscle and saphenous nerve stimulation suggest different transmitters involved or different sites of interaction of these inputs with the medullary respiratory rhythm generator.     

Influence of vibration on mechanical power and electromyogram activity in human arm flexor muscles

The aim of this study was to evaluate the influence of vibration on the mechanical properties of arm flexors. A group of 12 international level boxers, all members of the Italian national team, voluntarily participated in the experiment: all were engaged in regular boxing training. At the beginning of the study they were tested whilst performing forearm flexion with an extra load equal to 5% of the subjects' body mass. Following this. one arm was given the experimental treatment (E; mechanical vibration) and the other was the control (no treatment). The E treatment consisted of five repetitions lasting 1-min each of mechanical vibration applied during arm flexion in isometric conditions with 1 min rest between them. Further tests were performed 5 min immediately after the treatment on both limbs. The results showed statistically significant enhancement of the average power in the arm treated with vibrations. The root mean square electromyogram (EMGrms) had not changed following the treatment but, when divided by mechanical power, (P) as an index of neural efficiency, it showed statistically significant increases. It was concluded that mechanical vibrations enhanced muscle P and decreased the related EMG/P relationship in elite athletes. Moreover, the analysis of EMGrms recorded before the treatment and during the treatment itself showed an enormous increase in neural activity during vibration up to more than twice the baseline values. This would indicate that this type of treatment is able to stimulate the neuromuscular system more than other treatments used to improve neuromuscular properties.     

Influence of stimulation of the ocular muscles on the formation of visual responses of the lateral geniculate nucleus of the cat

In acute experiments on anesthetized cats it was shown that a single stimulation of the ocular muscles leads to unambiguous changes in the formation of the negative and positive components of the evoked response of the lateral geniculate nucleus to the presentation of a light stimulus. It was established that the nature of the muscular influences on the formation of these components of the evoked response of the lateral geniculate nucleus depends on the interval between conditioning muscular and test light stimuli.A. I. Karaev Institute of Physiology, Academy of Sciences of the Azerbaidzhan Republic, Baku. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 451–455, July–August, 1991.