Voluntary Muscular Activity Research Articles

The benefit of knowledge: postural response modulation by foreknowledge of equilibrium perturbation in an upper limb task.

For whole-body sway patterns, a compound motor response following an external stimulus may comprise reflexes, postural adjustments (anticipatory or compensatory), and voluntary muscular activity. Responses to equilibrium destabilization may depend on both motor set and a subject`s expectation of the disturbing stimulus. To disentangle these influences on lower limb responses, we studied a model in which subjects (n = 14) were suspended in the air, without foot support, and performed a fast unilateral wrist extension (WE) in response to a passive knee flexion (KF) delivered by a robot. To characterize the responses, electromyographic activity of rectus femoris and reactive leg torque was obtained bilaterally in a series of trials, with or without the requirement of WE (motor set), and/or beforehand information about the upcoming velocity of KF (subject`s expectation). Some fast-velocity trials resulted in StartReact responses, which were used to subclassify leg responses. When subjects were uninformed about the upcoming KF, large rectus femoris responses concurred with a postural reaction in conditions without motor task, and with both postural reaction and postural adjustment when WE was required. WE in response to a low-volume acoustic signal elicited no postural adjustments. When subjects were informed about KF velocity and had to perform WE, large rectus femoris responses corresponded to anticipatory postural adjustment rather than postural reaction. In conclusion, when subjects are suspended in the air and have to respond with WE, the prepared motor set includes anticipatory postural adjustments if KF velocity is known, and additional postural reactions if KF velocity is unknown.

Reduced Interhemispheric Coherence in Cerebellar Kainic Acid-Induced Lateralized Dystonia.

The execution of voluntary muscular activity is controlled by the primary motor cortex, together with the cerebellum and basal ganglia. The synchronization of neural activity in the intracortical network is crucial for the regulation of movements. In certain motor diseases, such as dystonia, this synchrony can be altered in any node of the cerebello-cortical network. Questions remain about how the cerebellum influences the motor cortex and interhemispheric communication. This research aims to study the interhemispheric cortical communication between the motor cortices during dystonia, a neurological movement syndrome consisting of sustained or repetitive involuntary muscle contractions. We pharmacologically induced lateralized dystonia to adult male albino mice by administering low doses of kainic acid on the left cerebellar hemisphere. Using electrocorticography and electromyography, we investigated the power spectral densities, cortico-muscular, and interhemispheric coherence between the right and left motor cortices, before and during dystonia, for five consecutive days. Mice displayed lateralized abnormal motor signs, a reduced general locomotor activity, and a high score of dystonia. The results showed a progressive interhemispheric coherence decrease in low-frequency bands (delta, theta, beta) during the first 3 days. The cortico-muscular coherence of the affected side had a significant increase in gamma bands on days 3 and 4. In conclusion, lateralized cerebellar dysfunction during dystonia was associated with a loss of connectivity in the motor cortices, suggesting a possible cortical compensation to the initial disturbances induced by cerebellar left hemisphere kainate activation by blocking the propagation of abnormal oscillations to the healthy hemisphere. However, the cerebellum is part of several overly complex circuits, therefore other mechanisms can still be involved in this phenomenon.

Facial Nerve Intraoperative Monitoring in Otologic Surgeries under Sedation and Local Anesthesia – A Case Series and Literature Review

Introduction Local anesthesia with sedation has been employed for an increasingly number of otolaryngology procedures, and might be associated with lower surgical morbidity and costs. Facial nerve monitoring is often advisable in otology to minimize the risks of injuries to this cranial nerve, but the principles, techniques and parameters involved have only been studied for procedures under general anesthesia. Objective To report the preliminary outcomes of intraoperative facial nerve monitoring during otologic procedures under sedation and local anesthesia. Methods A total of five procedures and their respective intraoperative electrophysiological main findings were described. Facial neuromonitoring was performed using the same device by an electrophysiologist. The monitor sensitivity was set at 100 mV, and a stimulating probe was used whenever needed. Results Progressively decreasing low-amplitude baseline values were usually obtained as the level of anesthesia increased, with isolated oscillations possibly related to some degree of voluntary muscular activity. These oscillations could be easily distinguished from those of the surgical manipulation or electrical stimulation of the nerve, which tended to be of much greater amplitude and shorter latency, occurring during specific surgical steps. Conclusion With a surgical team with proper procedural knowledge and broad expertise regarding the technique, intraoperative facial nerve monitoring under local anesthesia with sedation seemed both feasible and reliable. Thus, the need for intraoperative neuromonitoring should not be an obstacle for otologic procedures under less aggressive anesthetic management.

Vibration-related extrusion of capillary blood from the calf musculature depends upon directions of vibration of the leg and of the gravity vector.

In this study, we investigated the effects of vibration of the whole lower leg on the content and the oxygenation of hemoglobin in the unloaded relaxed lateral gastrocnemius muscle. Vibration was applied orthogonal to and in parallel with leg axis to examine whether the extrusion of blood depends on an alignment of main vessel direction, axis of vibration and gravity. The blood volume in the muscles was altered by horizontal and 30° upright body posture. Fifteen male subjects were exposed to 4 sets of experiments with both vibration directions and both tilt angles applied in permutated order. The absence of voluntary muscular activity and the potential occurrence of compound action potentials by stretch reflexes were monitored using electromyography. Total hemoglobin and tissue saturation index were measured with near infrared spectroscopy. Changes of lower leg circumference were measured with strain gauge system placed around the calf. Vibration caused decrease in tHb and increase in TSI indicating extrusion of predominantly venous blood from the muscle. In 30° tilted position, muscles contained more blood at baseline and vibration ejected more blood from the muscle compared with horizontal posture (p < 0.01). At 30° tilting deeper drop in tHb and steeper increase in TSI (p < 0.01) were observed when vibration was applied in parallel with the length axis of muscle. It is concluded that the vibration extrudes more blood in 30° head up posture and the vibration applied in parallel with the length axis of the muscle is more effective than orthogonal vibration.

Study of exteroceptive suppression of voluntary muscular activity in healthy volunteers and patients with paroxysmal neuropathic pain.

The exteroceptive suppression of voluntary electromyographic activity of the masseter and temporal muscles was studied in healthy volunteers and patients with paroxysmal neuropathic pain (trigeminal neuralgia). The latent period of the exteroceptive suppression was prolonged and the duration of its late fragment was shortened in the patients in comparison with normal subjects. A short exteroceptive suppression period in patients with trigeminal neuralgia reflected deficient activity of inhibitory interneurons of the reflector loop and excessive activity of the antinociceptive system of the brain stem, while prolongation of the latent period reflected prolongation of inhibitory interneurons activation. A direct correlation between the degree of changes in the exteroceptive suppression parameters and pain intensity, evaluated by the patients by the visual analog scale, was detected.

Biophysical and Physiological Basis of Human Cold Acclimatization

On exposure to cold, the problem is to maintain internal temperature of the human body in the presence of an increased thermal gradient between the core and the external environment. The ability to maintain homeothermy in the cold environment is enhanced in the acclimatized man. Superimposed upon the adaptive responses of the whole body to cold exposure are the adaptive responses of the extermities to avoid severe cold injury. The two major methods of adjustment to cold exposure are metabolic adjustments and peripheral cooling. Metabolic adjustment involve an increase in heat production in response to a cold stress such as shivering and non shivering thermogenesis and voluntary muscular activity. Peripheral cooling reduce the loss of heat from the skin by effectively increasing the thickness of relatively cooler peripheral tissues. The available literature on human cold acclimatization has been surveyed with a view to explain the biophysical and physiological mechanisms involved in the process of acclimatization.

Silent Period-Dentate, Edentulous, and Patients With Craniomandibular Dysfunction

The record of electrical activity of elevator muscles in mandible is important for the evaluation of muscular potency and diagnosis of neuromuscular pathologies, which allows prevention and treatment. The aim of this study was to define silent periods (SPs) and the importance in dentistry and compare the SPs in masticatory muscles of dentate and edentulous patients wearing prosthesis considering the presence or absence of craniomandibular dysfunction (CMD). Literature review in PubMed database. Silent periods are isolated pulses of transcranial magnetic stimulation in the primary motor cortex during voluntary muscular activity that generates an interruption of muscular activity for hundredths of milliseconds. The SP duration depends on the patient (dentate or edentulous), type of stimulus, and presence of CMD. The SP is higher in complete edentulous patients and in individuals with occlusal disharmonies than in dentate patients without CMDs. The treatment of CMDs through occlusal therapy decreases SP duration.

Effect of voluntary periodic muscular activity on nonlinearity in the apparent mass of the seated human body during vertical random whole-body vibration

The principal resonance frequency in the driving-point impedance of the human body decreases with increasing vibration magnitude—a nonlinear response. An understanding of the nonlinearities may advance understanding of the mechanisms controlling body movement and improve anthropodynamic modelling of responses to vibration at various magnitudes. This study investigated the effects of vibration magnitude and voluntary periodic muscle activity on the apparent mass resonance frequency using vertical random vibration in the frequency range 0.5–20 Hz. Each of 14 subjects was exposed to 14 combinations of two vibration magnitudes (0.25 and 2.0 m s −2 root-mean square (rms)) in seven sitting conditions: two without voluntary periodic movement (A: upright; B: upper-body tensed), and five with voluntary periodic movement (C: back-abdomen bending; D: folding-stretching arms from back to front; E: stretching arms from rest to front; F: folding arms from elbow; G: deep breathing). Three conditions with voluntary periodic movement significantly reduced the difference in resonance frequency at the two vibration magnitudes compared with the difference in a static sitting condition. Without voluntary periodic movement (condition A: upright), the median apparent mass resonance frequency was 5.47 Hz at the low vibration magnitude and 4.39 Hz at the high vibration magnitude. With voluntary periodic movement (C: back-abdomen bending), the resonance frequency was 4.69 Hz at the low vibration magnitude and 4.59 Hz at the high vibration magnitude. It is concluded that back muscles, or other muscles or tissues in the upper body, influence biodynamic responses of the human body to vibration and that voluntary muscular activity or involuntary movement of these parts can alter their equivalent stiffness.

Modulation of a motor evoked response to transcranial magnetic stimulation by the activity level of the first dorsal interosseous muscle in humans when grasping a stationary object with different grip widths

A relation between corticospinal excitability and background voluntary muscular activity was investigated at low and high transcranial magnetic stimulation (TMS) intensities while grasping a stationary object with different widths (2 and 8 cm) using a precision grip. The muscle activity was recorded from the first dorsal interosseous muscle. Regression analysis revealed that there was a linear relation between the motor evoked potential (MEP) and background muscular activity for both grip widths at each of the TMS intensities. At the low TMS intensity, the slope of the regression lines was similar for the 2 and 8 cm grip widths. It was, however, different when the TMS intensity was high. The results suggested that sensitivity modulation of bias level (input) facilitation occurred with wider grip width. The results of this study would reflect to quantitative aspects of the relation between the synaptic drive to the motoneuron pool and the resulting efferent activity characterized, i.e. input–output relations of the human corticospinal pathway dependent on the occasion demand.

Torque history of electrically stimulated human quadriceps: implications for stimulation therapy.

The time course of knee extension torque was measured in human quadriceps muscles during 30 min of transcutaneous neuromuscular electrical stimulation (NMES). Ninety subjects were divided into six experimental groups (n = 15 per group), which received stimulation at one of the following frequency/duty cycle combinations: 10 Hz/50%, 30 Hz/50%, 50 Hz/50%, 10 Hz/70%, 30 Hz/70%, and 50 Hz/70%. Two-way analysis of variance revealed that the magnitude of the relative torque decrease (the percentage of decrease in torque relative to the initial value) was significantly different between frequencies (p < 0.005) and duty cycles (p < 0.02), with no significant interaction (p > 0.6). Increasing either frequency or duty cycle caused a greater decrease in torque. In spite of this result, there was no significant difference between groups in the total activity (torque-time integral) achieved during the 30 min treatment session. The magnitude of this activity corresponded to only about 7-14 maximum voluntary contractions. Finally, the average torque during the treatment session was significantly different among groups (p < 0.001), being greatest for the 50 Hz/50% group and least for the 10 Hz/70% group. Taken together, these data suggest that a smaller number of longer duration contractions produces the greatest muscle tension. They also suggest that the absolute torque levels achieved with NMES are relatively low compared with voluntary muscular activity.

Energetics and Development of Temperature Regulation in Capercaillie Tetrao urogallus

Thermoregulatory capacities of newly hatched and developing capercaillie chicks (Tetrao urogallus) were studied. Metabolic rate and body temperature measurements were conducted at ambient temperatures ($T_{a}$) between -30 and 37 C. The chicks rely primarily on behavioral thermoregulation. A sudden increase of basal heat production at the age of 4-5 days constitutes an important element in the control of stable body temperature ($T_{b}$) and coincides with the gradual elevation of the body temperature and capacity to stimulate thermoregulatory heat production. Chicks 1-3 days old can more than double their metabolic rate at 15 C. There is no evidence of regulatory nonshivering thermogenesis. Consequently, the only way to increase heat production is to stimulate muscular activity either by shivering or by voluntary muscular activity. The most rapid development of thermoregulatory capacity occurs at the age of 7-11 days, which may be correlated with the synergistic maturation of neuronal thermoregulatory co...

Leucine and urea metabolism in acute human cold exposure.

Four healthy males voluntarily underwent acute cold exposure at 10 degrees C. Metabolic rate doubled for the 100-min exposure. [1-13C]leucine and [15N2]urea were used as tracers of protein metabolism via a primed constant infusion. Total and plasma transported leucine oxidation approximately doubled, but the oxidation of leucine derived from protein in the tissue where oxidation occurred ("intracellular oxidation") did not change as it did when the same subjects underwent mild exercise. Rate of appearance of urea and leucine in plasma were not significantly different between control and cold. Although the rate of protein synthesis calculated from the leucine data did not change, the rate of catabolism increased. Net protein catabolism based on the urea data agreed well with the leucine data at rest but did not exhibit a significant increase during exposure. However, net protein catabolism based on the leucine data did increase significantly during acute cold exposure. Further, there appears to be a qualitative difference in the protein catabolism associated with the voluntary muscular activity of exercise and muscular shivering aimed at thermogenesis.

Phosphorylase a in human skeletal muscle during exercise and electrical stimulation.

Experiments were conducted to examine the conversions of phosphorylase b to phosphorylase a in human skeletal muscle during bicycle exercise or isometric contractions. Muscle biopsies were obtained from the vastus lateralis with the needle technique at rest and either during or immediately after activity and frozen in liquid nitrogen within 2--4 s. Total phosphorylase and phosphorylase a activities were differentiated by measurement in the presence and absence of AMP, respectively. At rest 8.5% of the total phosphorylase activity existed in the a form. Little or no change in the percent of phosphorylase in the a form occurred during voluntary dynamic or static muscular activity that produced muscle lactate concentrations in excess of 18 mmol.kg-1 wet muscle. Electrical stimulation of the vastus lateralis muscle also failed to produce an increase in the percentage of phosphorylase a. These data suggest that during exercise the conversion of phosphorylase to the a form is of minor importance. An increased activity of phosphorylase b due to changes in muscle concentrations of ATP, AMP, and inorganic phosphate may regulate glycogenolysis during voluntary exercise in man.

Isaacs' syndrome. Report of a case and review of the literature

The case of a 17-year-old boy who had been well until the age of four when progressive stiffness of lower limbs developed is reported. Soon walking became difficult and on on his thighs, buttocks and calves one could notice the appearance of myokymia. Painful and intermittent spasms were often present specially after physical strain. This was followed by profuse sweating. Strength was normal but muscle relaxing was slow mainly in the quadriceps. The familiar history for neuromuscular pathology was negative. Muscle enzymes, thyroid function tests were within normal limits and muscular biopsy showed no abnormalities. The EMG disclosed a permanent spontaneous activity, more evident in the quadriceps, which was normal in shape, amplitude and duration. In association to this activity multiplets discharges and low motor units were also observed; in interferencial pattern appeared at maximum contraction but the multiplets and low motor units potentials kept on showing even though voluntary muscular activity ceased. The therapeutic essay with carbamazepin had a dramatic effect upon the course of the patient's conditions. He showed a great improvement with this drug and today leads a normal life being able even to play soccer and ride a bicycle. An interesting remark which should be done is the fact that the flexion of the neck inhibits the quadriceps myokymia whereas the extension makes them to appear and even worsen. Unfortunately is was not possible to carry out a more accurate investigation concerning electropharmacology and hystopathology as the patient was uncooperative and refused to undergo such examinations. However the authors believe that this clinical picture can be considered as a case of "continuous muscle-fibre activity" due to the great similarity it bears to the cases related by Isaacs in 1961. An extensive review concerning the pertinent literature has been done.

The maximum metabolic response of sheep to cold: effects of rectal temperature, shearing, feed consumption, body posture, and body weight

Shorn, adult sheep were exposed to an ambient temperature of about 1°C and a rate of fall in rectal temperature of 0.5–2.0°C/hr was obtained by varying wind velocity and wetness of the fleece. Respiratory gaseous exchange was monitored continuously, and the records were used to calculate metabolic rate. The maximum instantaneous metabolism was 2–36% higher than the maximum metabolism averaged over a 20 min period-termed summit metabolism. Since the larger differences were due to an additive effect of voluntary muscular activity, summit metabolism was adopted as the estimate of the maximum metabolic response to cold. There was no consistent relation between summit metabolism and rectal temperatures above 37°C, but there was a direct relationship at rectal temperatures between 30 and 37°. Shearing the sheep just prior to a determination, or fasting the animal for 19–21 hr, did not influence the magnitude of the summit metabolism. Fasting for 3 days reduced the maximum response by an amount equal to the heat increment of the ration. Sheep generally remained standing during the exposure to extreme cold. While the sheep were lying down, summit metabolism was 26–28% lower than the value during standing, and heat production was reduced to a greater extent than heat loss, since the rate of fall in rectal temperature was greater than that during standing. Summit metabolism was proportional to fleece-free body weight raised to the power 0.9, and summit metabolism per unit of surface area increased with increasing body weight. When sheep were housed in a warm or thermoneutral environment prior to the tests to prevent acclimatization to cold, their summit metabolism averaged 10 watts/kg or 25 watts/kg0.75 and day to day variation in individual sheep was about 6%.

Power spectral shifts in hippocampal EEG associated with conditioned locomotion in the rat

Hippocampal bioelectrical activity and bodily movements were monitored in water-deprived naive male rats who were subsequently trained to increase gross voluntary muscular activity beyond base-line levels by running back and forth in testing chamber for water reward. This procedure led to a marked increase in theta wave activity in the hippocampus. Extinction of the behavioral response was paralleled by a decline toward base-line levels of movement and theta wave activity. Reconditioning of hyperactivity led to a concomitant increase in theta activity as recorded from the hippocampus.

A contribution to the toxicological evaluation of hexamethylenetetramine

Hexarnethylenetetramine (Hexa) has been studied in a long-term trial in which rats were fed on a diet containing 0·16% Hexa from weaning to natural death. The voluntary muscular activity, body-weight curves, lifespan, causes of death and the relative weights of major organs were compared with those of rats fed the same diet without added Hexa. No differences between the test groups and the control groups could be detected. In a palatability experiment, rats were allowed to choose between food containing Hexa and the same food without Hexa for a 28-day period. The two types of food were consumed in comparable amounts. After a 120-day period during which they were fed only the Hexa diet, all the rats were allowed to choose between the two diets in a second 28-day trial. Again the rats revealed no dislike of the Hexa diet. The fertility of the Hexa-treated rats was similar to that of the controls, and the young of the second generation, fed like their parents on the Hexa diet, did not differ from the offspring of the control rats with regard to voluntary muscular activity, body weights, general health and relative organ weights.

USE OF DAILY METABOLIC PERIODICITIES AS A MEASURE OF THE ENERGY EXPENDED BY VOLUNTARY ACTIVITY OF MICE

At temperatures of 10, 20, and 30 °C., average metabolism of 12 mice in small respiration chambers was significantly greater during the night than during the day but was sensibly the same at night and day when constant work levels were imposed in a treadmill apparatus. In these tests the increase in metabolism due to work varied only slightly, if at all, with temperature. It is concluded that diurnal variation in metabolism in the small chambers resulted mainly from variation in voluntary muscular activity. On this supposition, it is estimated that the energy expended in voluntary activity averaged 2350 cal. per mouse per 24 hr. at all these temperatures, which was 12, 16, and 27% of the total daily expenditure at 10, 20, and 30 °C. respectively.

Relationship Between Spontaneous Activity and Metabolic Rate as Influenced by Certain Sympathomimetic Compounds

SummaryComparisons were made between the oxygen consumption and increased movements induced by the central nervous excitatory effects of a number of physiologically active organic compounds. After injection of several of these compounds, benzedrine, desoxyephedrine and N-methyl-β-cyclohexylisopropylamine HCl, oxygen consumption and voluntary movements varied in direct relationship to each other. After the injection of another compound (Isuprel), oxygen consumption increased greatly, but there was a decrease in activity. Oxygen consumption can be used as a measure of voluntary muscular activity only under limited conditions.

THE RELATION OF EXERCISE TO BUBBLE FORMATION IN ANIMALS DECOMPRESSED TO SEA LEVEL FROM HIGH BAROMETRIC PRESSURES

1. Bullfrogs (Rana catesbiana) and rats have been subjected to high barometric pressures and studied for bubble formation on subsequent decompression to sea level. Pressures varying from 3 to 60 pounds per square inch, in excess of atmospheric pressure, were used. 2. Muscular activity after decompression is necessary for bubble formation in bullfrogs after pressure treatment throughout the above range. Anesthetized frogs remained bubble-free following decompression. Rats compressed at 15 to 45 pounds per square inch likewise did not contain bubbles unless exercised on return to sea level. 3. Bubbles form without voluntary muscular activity in anesthetized rats previously subjected to pressure of 60 pounds per square inch. Small movements involved in breathing and other vital activities are believed sufficient to initiate bubbles in the presence of very high supersaturations of N(2). 4. Bubbles appear (with exercise) in rats previously compressed at 15 pounds per square inch, and in bullfrogs subjected to pressure at levels as low as 3 pounds per square inch above atmospheric pressure. The percentage drop in pressure necessary for bubble formation is less in compressed animals than in those decompressed from sea level to simulated altitudes. 5. The action of exercise on bubble formation in compressed frogs and rats is attributed to mechanical factors associated with muscular activity, combined with the high supersaturation of N(2). CO(2) probably is not greatly involved, since its concentration does not reach supersatuation, as it does at high altitude. 6. Anoxia following decompression from high barometric pressures has no observable facilitating effect on bubble formation.