Activation of shoulder muscles in healthy men and women under isometric conditions

Purpose: Due to the low osseous lead of the shoulder joint a large portion of the shoulder muscles, in addition to executing movements, deals with stabilising tasks. This requires a permanent readjustment of the intermuscular co-ordination of all involved muscles. The aim of the study was to verify the existence of gender dependent differences in intramuscular co-ordination patterns of shoulder muscles.

Method: Fifteen healthy men and nine healthy women, who executed 24 isometric exercises in sagittal, frontal and horizontal planes with a loading of 50% of their individual isometric maximum force, were investigated. In every plane, four angular positions were chosen and both opposite force directions were measured, respectively. SEMG was taken from 13 muscles of the shoulder and the upper arm. Due to inter-individual differences SEMG amplitudes were normalised. Results: Gender specific differences of functional intermuscular co-ordination patterns could be proven systematically. Women showed less activation of muscles acting in the main force direction. In addition, those muscles less necessary for the actual force production were more activated in women than in men.

Conclusions: Functionally comparable shoulder function showed a gender dependency in terms of functional intermuscular co-ordination.     

Activation of walking by electrical stimulation in humans under the conditions of muscle unloading and its variations under the effect of afferent influences

The possibility of initiating an involuntary walking rhythm in a suspended human leg by electrical stimulation was studied. The subjects lay on the side with one leg suspended in an exoskeleton allowing horizontal rotation in three joints: the hip, knee, and ankle ones. To evoke involuntary walking of the suspended leg, two methods were used: continuous vibration of the quadriceps muscle of the hip and electrical stimulation of the cutaneous nerves innervating the foot of the immobile leg. The hip and ankle were involved in the involuntary movements, with reciprocal bursts of electromyographic activity being also observed in the antagonistic muscles of the hip. The application of an external load (4 N or 8 N) to the foot caused a perceptible intensification of its movements. An additional weight (0.5 kg) or a rubber band wrapped around the foot caused no substantial change in the pattern of stimulated walking. Electrical stimulation is an effective means of activating walking movements, and their characteristics confirm the assumption that the walking rhythm is of central origin. Additional afferentation from the sole’s receptors plays an important role in the modulation of the induced movements and the modification of the general walking pattern under the conditions of muscle unloading.     

Changes in the somatosensory evoked potentials in the night sleep of healthy subjects under conditions of preceding emotional stress

Somatosensory evoked potentials (SEP) were studied in eight healthy subjects in a state of alertness, in different stages of night sleep and also in night sleep after previous emotional stress. Characteristic changes of SEP were revealed in the second stage of sleep in delta-sleep and in the phase of rapid sleep. In conditions of emotional stress changes in SEP characteristics in periods of alertness and of night sleep were observed, expressed in the amplitude increase of a number of components. Asymmetry was revealed with predominance of the amplitude increase in the right hemisphere in the phase of the rapid sleep testifying to different roles of the cerebral hemispheres in processing of emotionally significant information. SEP changes in different functional states after the influence of emotional stress were considered as the reflection of non-specific activation increase possibly due to activation of the limbic structures in response to stress-producing stimulus.     

Anticipatory postural adjustment in bimanual unloading: role of the motor cortex in motor learning

The role of the motor cortex was investigated during learning unusual postural adjustment. Healthy subjects held their right (postural) forearm in a horizontal position while supporting a 1-kG load via an electromagnet. The postural forearm position was perturbed by the load release triggered by other elbow voluntary movement. Repetition of the imposed unloading test resulted in a progressive reduction of the maximal forearm rotation, accompanied by the anticipatory decrease in m. biceps brachii activity (learning). Control situation consisted of the voluntary forearm loading. Using the transcranial magnetic stimulation we examined changes in the motor evoked potential of the m. biceps brahii at the beginning and at the end of learning. The evoked potential amplitude did not significantly change in process of the decrease of m. biceps brachii activity. At the end of learning, motor evoked potential / baseline electromyogram ratio increased as compared to the beginning of learning and to the control situation. The results highlight the fundamental role of the motor cortex in suppression of synergies which interfere with formation of a new coordination during motor learning.     

Changes in the transcutaneous oxygen and carbon dioxide tension during the ischemic test in healthy subjects and under conditions of chronic ischemia of the limb

Changes in the transcutaneous oxygen and carbon dioxide tension during the ischemic test and subsequent reactive hyperemia for 1–2 min in healthy men occur in counterphases. A maximal increase in the carbon dioxide content occurs during the first minute after ischemia. Under conditions of chronic ischemia of the limb, changes in the transcutaneous oxygen and carbon dioxide tension are similar to those in healthy men, but the time intervals are changed and the relative increase in the carbon dioxide content is higher.     

Effects of alprazolam and clonidine on carbon dioxide-induced increases in anxiety ratings in healthy human subjects

In order to investigate possible neurobiologic mechanisms underlying carbon dioxide-induced anxiety, the effects of oral alprazolam 0.75 mg and intravenous clonidine 2 mcg/kg on CO2-induced increases in ratings of subjective anxiety, pulse rate, and ventilation were measured in healthy human subjects. Pretreatment with alprazolam but not with clonidine significantly reduced the CO2-induced increase in ratings of anxiety. Neither drug altered CO2-induced increases in pulse rate or ventilatory responses. Clonidine did produce potent sedative and hypotensive effects. The behavioral data suggest that the mechanisms through which CO2 induces anxiety-like effects involve neural systems regulated by benzodiazepine receptors and, secondly, that they appear not to require normal functioning of noradrenergic systems. Carbon dioxide may provide a useful model system for identification of new drugs with anxiolytic properties.     

Application of transcranial magnetic stimulation for monitoring of the motor cortex condition in dynamics in healthy subjects

Transcranial magnetic stimulation (TMS) is used already for sixteen years for studying human central nervous system. The main objective of this work was to study motor thresholds and their hemispheric asymmetry in healthy subjects during TMS. We examined 31 righthanded healthy students. Their motor thresholds were measured in May (before vacations), September (immediately after vacations), and November (two months after vacations). Magnetic stimulator Neurosoft-MS (Ivanovo, Russia) was used for TNS of the motor cortex. It was shown that in the absence of regular active functional loads on the right hand, the motor thresholds in healthy righthanders significantly increased under the TMS of the left hemisphere, and hemispheric asymmetry disappeared under conditions both of muscle relaxation and voluntary contraction. Motor thresholds under the left-side TMS decreased and hemispheric asymmetry recovered with the restart of the regular active functional loads on the right hand.     

The results of a serological study of viral hepatitis patients and healthy subjects under the conditions of a high-intensity epidemic process in hepatitis A

The activity of the involvement of preschool children of different ages in organized groups into the epidemic process of hepatitis A and the state of population immunity in elderly persons have been studied. Under the conditions of the intensive development of the epidemic process the active involvement of preschool children into this process as early as at the age of 1-2 years has been noted. At periods between epidemics the active circulation of the infective agent in the presence of decreased manifestations of the disease has been revealed.     

Comparison of the aerobic performance of leg and arm muscles in cross-country skiers

In the last fifteen years, a trend has appeared in cross-country ski racing to increase the use of double poling and, therefore, to increase the load on the shoulder girdle (arm) muscles. The purpose of this study was to compare the aerobic performance of elite cross-country skiers in incremental running (treadmill) and double poling (with manual ski ergometer) tests to exhaustion. Four junior cross-country skiers and four biathletes ( $ \dot V_{O_{2max} } $ = 70 (66?C72) mL/min per kg body weight) participated in the experiment. In the double poling test, the lactate concentration increased more rapidly than in the running test, and the peak oxygen consumption ( $ \dot V_{O_{2peak} } $ ) in the double poling test was 88 (84?C93)% of the maximal oxygen consumption ( $ \dot V_{O_{2max} } $ ) in the running test. The relative anaerobic threshold, which characterizes the relative level of current aerobic performance, in the double poling test was significantly lower than in the running test (79 (57?C83)% vs 94 (90?C98)%, respectively). On the basis of these data, it can be concluded that the main reserve for a further increase in the aerobic performance of cross-country skiers and biathletes is the increase in the aerobic capacity of arm and trunk muscles.     

Voluntary stepping behavior under single- and dual-task conditions in chronic stroke survivors: A comparison between the involved and uninvolved legs

ObjectiveIf balance is lost, quick step execution can prevent falls. Research has shown that speed of voluntary stepping was able to predict future falls in old adults. The aim of the study was to investigate voluntary stepping behavior, as well as to compare timing and leg push-off force–time relation parameters of involved and uninvolved legs in stroke survivors during single- and dual-task conditions. We also aimed to compare timing and leg push-off force–time relation parameters between stroke survivors and healthy individuals in both task conditions.MethodsTen stroke survivors performed a voluntary step execution test with their involved and uninvolved legs under two conditions: while focusing only on the stepping task and while a separate attention-demanding task was performed simultaneously. Temporal parameters related to the step time were measured including the duration of the step initiation phase, the preparatory phase, the swing phase, and the total step time. In addition, force–time parameters representing the push-off power during stepping were calculated from ground reaction data and compared with 10 healthy controls.ResultsThe involved legs of stroke survivors had a significantly slower stepping time than uninvolved legs due to increased swing phase duration during both single- and dual-task conditions. For dual compared to single task, the stepping time increased significantly due to a significant increase in the duration of step initiation. In general, the force time parameters were significantly different in both legs of stroke survivors as compared to healthy controls, with no significant effect of dual compared with single-task conditions in both groups.ConclusionsThe inability of stroke survivors to swing the involved leg quickly may be the most significant factor contributing to the large number of falls to the paretic side. The results suggest that stroke survivors were unable to rapidly produce muscle force in fast actions. This may be the mechanism of delayed execution of a fast step when balance is lost, thus increasing the likelihood of falls in stroke survivors.     

Electromyographic latency of postural evoked responses from the leg muscles during EquiTest Computerised Dynamic Posturography: Reference data on healthy subjects

No normative data are available for the latencies of the EMG signals from the ankle muscles in response to sudden sagittal tilt (toes-UP or toes-DOWN) or shift (shift-FOR or shift-BACK) of the support surface during standing. In this study the postural evoked response (PER) paradigm on the EquiTest™ force platform was applied to 31 healthy adults (18 women and 13 men; mean age 29 years). The EMG latencies (PEREMG) were computed both through the standard manual procedure and through a specially designed automated algorithm. The manually computed PEREMG onset yielded a 95% tolerance interval between 82 ms and 148 ms after toes-UP perturbation, between 93 ms and 182 ms after toes-DOWN perturbation, between 67 ms and 107 ms after shift-BACK perturbation, and between 73 ms and 113 ms after shift-FOR perturbation. When comparing the two methods, paired t-tests showed no significant mean difference (Bonferroni-adjusted p-values ranged from 0.440 to 1.000) and all Bland–Altman plots included zero difference within the limits of agreement. Therefore, the manual and the automated methods appear to be sufficiently consistent. These results foster the clinical application of PEREMG testing on the EquiTest platform.     

Resistance and hemodynamic reactions in healthy pilots under the conditions of passive orthostatic loading

The results of the analysis of materials on the expert assessment of 66 healthy pilots subjected to a passive orthostatic stress test (POT) by the generally accepted technique of a 20-min head-down tilt bed rest at an angle of 80° to the horizontal are presented. The obtained hemodynamic responses to the test were typified using the generally accepted concepts of functional classes (FC). A good POT tolerance was recorded in 86.4% of the observations, with 36.4% assigned to the first functional class (FC-I) and 50%, to the second functional class (FC-II). A satisfactory orthostatic test tolerance (FC-III) was recorded in 10.6% of the observations, whereas a reduced and poor tolerance (FC-IV and FC-V) was found in 3% of the observations. According to ECGs and computer-assisted tachooscillography, subjects of the FC-I group reached the optimum indicators in their adaptive hemodynamic responses, compared to the pilots of the FC-II group and, particularly, the FC-III group. The latter two groups were found to exhibit some previously unknown objective symptoms, such as marked blood pressure (BP) lability and reversible hypo- and hypertensive responses, which allowed us to differentiate the FC-I pilots from the latter two groups. Based on the obtained results, additional clinical functional tolerance assessment criteria have been developed for a passive orthostatic test as part of the medical expert assessment of flight personnel with different levels of functional stability.     

Activation timing of soleus and tibialis anterior muscles during sit-to-stand and stand-to-sit in post-stroke vs. healthy subjects

Introduction. Sit-to-stand (SitTS) and stand-to-sit (StandTS) are very important functional tasks that become compromised in stroke patients. As in other voluntary movements, they require an adequate postural control (PC) involving the generation of anticipatory postural adjustments (APAs). In order to give clues for more efficient and directed rehabilitation programs, a deeper knowledge about APAs during challenging and daily life movements is essential.

Purpose. To analyze the activation timing of tibialis anterior (TA) and soleus (SOL) muscles during SitTS and StandTS in healthy subjects and in post-stroke patients.

Methods. Two groups participated in this study: one composed of ten healthy subjects and the other by ten subjects with a history of stroke and increased H-reflex. Electromyographic activity (EMGa) of SOL and TA was analyzed during SitTS and StandTS in the ipsilateral (IPSI) and the contralateral (CONTRA) limb to the side lesion in stroke subjects, and in one limb in healthy subjects. A force plate was used to identify the movement onset.

Results. In both sequences, in the stroke group SOL activation timing occurred prior to movement onset, contrary to the pattern observed in the healthy subjects. Statistically significant differences were found in SOL activation timings between each lower limb of the stroke and healthy groups, but no significant differences were found between the IPSI and the CONTRA limb. The TA activation timing seems to be delayed in the CONTRA limb when compared to the healthy subjects and showed a better organization of TA timing activation in StandTS when compared to SitTS.

Conclusion. Compared to healthy subjects, APAs seem to be altered in both limbs of the post-stroke subjects, with the SOL activation timing being anticipated in both SitTS and StandTS.     

Functional characteristics of hemodynamics in adolescents under the conditions of different motor activities

The formation of functional systems in correspondence with the conditions of natural activity is the most important issue of developmental physiology. In this study, data on the assessment of the state of central and cerebral hemodynamics, as well as indices of spectral analysis of the heart rate’s variability (HRV) in adolescents depending on the level of motor activity has been collected and systematized. The possibility of integration of methods of rheoencephallography and cardiorythmography for the assessment of the characteristics of the ontogenetic formation of the cardiovascular system has been studied. Analysis of the formation of indices of hemodynamics during an academic year and the training cycle in swimmers and healthy adolescents who do not enroll in sports classes has been made. Changes in, and correlations between, the parameters of central hemodynamics and cerebral circulation, as well as parameters of HRV, have been detected. Analysis of the changes in the statistical indices of the cardiac rhythm in adolescents during an academic year on the basis of the qualitative and quantitative characteristics of the state of regulatory systems, as well as the determination of the direction of the response to the combination of academic loads and the factor of physical training, permitted a detailed study of changes that take place in some hemodynamic parameters in athletes and students, which is of particular importance for the diagnosis of their functional state.