Muscle In Man Research Articles

Evidence of shared, direct input to motoneurons supplying synergist muscles in humans

Cross-correlation techniques were used to test for the presence of shared, direct input to motoneurons innervating different synergist elbow flexor muscles in man. Motor unit activity was recorded intramuscularly from two elbow flexor muscles during steady isometric elbow flexion in normal and paretic subjects. To increase the probability of detecting weak synchrony, one of the intramuscular needles was positioned to record multiunit activity. Significant correlogram peaks were obtained in 25 57 runs in normal subjects, and the features of the correlograms were similar to those previously reported based on cross-correlation of two single units within the same muscle. Further, the characteristics of discharge synchrony measured in paretic stroke patients are consistent with other reports on the effects of stroke on synchrony among motoneurons belonging to the same pool, i.e. narrow correlogram peaks were rare in paretic subjects and significant correlogram peaks often had longer than normal durations.

Projections of group Ia afferents to motoneurons of thigh muscles in man.

Changes in the firing probability of single motor units in response to electrical stimulation of muscle nerves and to tendon taps were used to derive the projections of large muscle afferents to the motoneurons of various thigh muscles in man. Homonymous facilitation was demonstrated to virtually all of the sampled motor units of biceps (BI), semitendinosus (ST), vastus lateralis (VL) and vastus medialis (VM). Heteronymous facilitation was readily demonstrated between VM and VL but was never obtained from ST to BI and never unequivocally obtained from BI to ST. Reciprocal inhibition was demonstrated from femoral nerve afferents to all of the sampled units of BI, and ST but reciprocal inhibition of VM or VL was never obtained from BI afferents and infrequently from ST afferents. These projections of group I afferents in man show certain specific differences from those of the cat and baboon that may reflect the normal function of the limb.

Comparison between the alpha-adrenoceptors of aortic smooth muscle in man and other animal species

Comparison between the alpha-adrenoceptors of aortic smooth muscle in man and other animal species

Tonic neck reflexes on upper limb flexor tone in man

The asymmetric tonic neck reflexes on upper limbs in man have been studied by analyzing the changes in flexor carpi radialis H-reflex amplitude following body rotation around the longitudinal axis with a stationary head. In eight normal subjects 15 consecutive H-refledes were recorded from the right flexor carpi radialis muscle at each test position. The tested body rotation angles were 4, 8, 12, 16, and 20° both to the right side and to the left side. Before and after each test position 15 H-reflexes were recorded at 0°. The linear correlation coefficient r, computed by plotting the H-reflex amplitudes against the relevant body rotation angles, was significant in all the subjects. The FCR H-reflex amplitude increased with contralateral body rotation (i.e., ipsilateral head rotation) and decreased with ipsilateral body rotation (i.e., contralateral head rotation). It has been suggested that these findings, which are opposite to those observed in animal experiments, are the consequence of the acquired antigravity function of upper limb flexor muscles in man.

Calcium Antagonists and Skeletal-Muscle Function in Man

This investigation was undertaken to determine whether the calcium antagonists verapamil, nifedipine, and diltiazem have any effect on the strength and endurance of skeletal muscle in man. Eight healthy men, aged 19 to 26 years, were given six separate treatments of calcium antagonists plus two administrations of placebo in a randomized, double-blind study. Drug treatments included two dosage levels of verapamil (80 and 120 mg, qid), nifedipine (10 and 20 mg, qid), and diltiazem (90 and 120 mg, qid). During each drug treatment and while receiving placebo, the subjects' knee extension/flexion strength and endurance were measured by use of an isokinetic dynamometer, anaerobic power was measured by use of a cycle ergometer, and aerobic capacity was measured while subjects exercised on the treadmill. There were no significant differences between treatments for any of the tests of skeletal-muscle function. The results of this investigation support those of other investigations of the specific cardiac- and smooth-muscle effects of this class of drug in man.

A possible role of airway epithelium in modulating hyperresponsiveness.

1. In order to examine the role of airway epithelium in the responsiveness of smooth muscle in man, we measured the contractile responses to acetylcholine (ACh), histamine, and prostaglandin F2 alpha (PGF2 alpha) and the relaxation response to isoprenaline (Isop), in 48 bronchi obtained from 10 patients who received surgery. Responses were measured in the presence and absence of the epithelium. 2. Removal of epithelium (by rubbing the mucosa gently with forceps) significantly increased the contractile responses evoked by ACh, histamine and PGF2 alpha. 3. In contrast, removal of epithelium did not alter the relaxation response to Isop. 4. To clarify the mechanism underlying this epithelial inhibitory effect on smooth muscle contraction, we measured the contractile responses of dog trachea with the epithelium removed to increasing concentrations of ACh. After measuring the control response, we added about 0.1 g of the chopped epithelium in the organ chamber, and measured the response again. 5. After adding airway epithelium and incubating with tracheal strips, the contractile response of tracheal strips decreased significantly as compared to the control response. 6. These results show that airway epithelium possesses the ability to decrease the smooth muscle contraction to ACh, histamine and PGF2 alpha in man and dogs. 7. The mechanism of this inhibitory effect of the airway epithelium is not explained by a change in mechanical property of the airway nor the change in diffusion of these drugs to the smooth muscle across the epithelium. Thus, these results suggest that airway epithelium may have an important role in modulating smooth muscle tone, possibly by inactivation of these mediators, or by releasing an epithelium-derived relaxing factor.

Study of age changes in the motor units of the first dorsal interosseous muscle in man.

The effect of ageing on the threshold firing rate of motor units from the first dorsal interosseous muscle was investigated. Two groups of 9 healthy male subjects between the ages of 20-29 and 60-69 years took part in the study. The threshold firing rate of motor units in young subjects showed close agreement with previous observations. However, a significant decrease was found in the older age group and, in addition, these units showed a prolongation of their contraction times, confirming our previous findings from this muscle. These results are discussed in relation to changes previously reported in human skeletal muscle and may indicate a functional change of the muscle with age.

Noradrenaline spillover during exercise in active versus resting skeletal muscle in man.

Increases in plasma noradrenaline (NA) concentration occur during moderate to heavy exercise in man. This study was undertaken to examine the spillover of NA from both resting and contracting skeletal muscle during exercise. Six male subjects performed one-legged knee-extension so that all measurements could be made both in the exercising and in the resting leg. Subjects exercised for 10 min at each of 50% and 100% of the peak performance capacity of the leg. Leg blood flow was measured by thermodilution and blood samples were drawn for the determination of plasma NA and adrenaline, first in the resting leg and then in the exercising leg. To calculate NA spillover, the extraction of NA (NAe) or of adrenalin (Ae) is required: NAe was measured by repeating the experiment under constant [3H]NA infusion following a 40-min rest period. During exercise, NA spillover was significantly larger in the exercising leg than in the resting leg both during 50% and 100% leg exercise. These results suggest that contracting skeletal muscle may contribute to a larger extent than resting skeletal muscle to increasing the level of plasma NA during exercise. Contractile activity may influence the NA spillover from skeletal muscle by a presynaptic and/or postsynaptic influence on the sympathetic nervous activity to this tissue.

Reflex excitability of human soleus motoneurones during voluntary shortening or lengthening contractions.

1. We investigated the possibility that increase or decrease in the monosynaptic reflex excitability of the soleus muscle in man might play a role in matching the muscle mechanical output to the voluntary command aimed at performing isotonic contractions or relaxations, at various velocities. 2. Rectified and integrated electromyographic activity (e.m.g.) and the H reflex of soleus were measured during plantar flexions against a constant load (shortening contractions) or dorsal flexions resisting the load (lengthening contraction), performed without activation of pretibial muscles. 3. At the same ankle joint angle, integrated e.m.g. was larger during shortening contractions than during lengthening contractions. During shortening contractions, integrated e.m.g. increased as a function of the velocity of plantar flexion. During lengthening contractions, integrated e.m.g. decreased as a function of dorsal flexion and angular velocity and nearly disappeared in the last part of the most rapid lengthening contractions. 4. During shortening contractions, the H reflex increased beyond the extent expected for the level of e.m.g. activity; during lengthening contractions, reduction of the H reflex below control values at rest occurred in spite of background e.m.g. activity. 5. When the level of e.m.g. activity was kept constant, the above changes in H reflex were larger in both directions as a function of the velocity of the movement. 6. Passive rotation in the dorsal direction contributed to the inhibition observed during lengthening contractions. 7. It is suggested that these changes in the excitability of the H reflex, probably presynaptic in origin, serve the purpose of appropriately modulating the rate and extent of motoneurone recruitment during shortening and lengthening contractions. This allows the foot to follow a constant-velocity path in spite of the perturbing effects of the spindle afferent inputs and of the muscle characteristics described by the force--length and force--velocity diagrams.

Jaw opening reflex activity in the inferior head of the lateral pterygoid muscle in man : Widmer CG. Arch Oral Biol 32:135, 1987

Jaw opening reflex activity in the inferior head of the lateral pterygoid muscle in man : Widmer CG. Arch Oral Biol 32:135, 1987

Functional property of the masseter muscle in man

The purpose of this paper is to investigate the functional property of the masseter muscle at the motor unit level in man. The responses of the surface EMG and the bite force were studied by averaging technique, with the following results.1. The higher threshold units with large twitch tensions were found in the superficial layer of the muscle, the lowers were throughout the muscle.2. Positive correlation was found between voluntary threshold force and peak twitch tension, linear correlation coefficient was 0.76.3. The motor units with a larger twitch tension tended to have shorter contraction time, but those of smaller had the wide range.4. There was a tendency for deeper-layer units to contribute less to the wave form of the surface EMG than did the superficial units.5. There was a significant tendency for the units recruited with larger forces to contribute extensively to the surface EMG. The linear correlation coefficient was 0.70.6. In 106 force records, DEM (the discrepancy between electrical activity and mechanical contraction) was observed. It seemed that DEM was similar phenomenon to the latency relaxation.

A comparison of electromyography recorded parallel and transverse to the fibres of the anterior and posterior temporalis muscle in man

Electrical activity recorded during voluntary clenching by platinum hook intra-cutaneous electrodes was significantly higher ( p < 0.01) when the electrodes were placed parallel to the muscle fibres than across the fibres. The correlation between the parallel and transverse EMG recordings was highly significant ( p < 0.001).

Morphologie und Innervation der Musculi levatores costarum bei Hund, Katze, Pferd und Schwein

In the anatomical literature there are inconsistencies in the description of the levatores costarum muscles in man and in the domestic animals, and their innervation either by the dorsal or the ventral branches of the thoracic nerves. Therefore we studied the form, structure and, with the aid of the dissecting microscope, the innervation of these muscles in 7 dogs, 8 cats, 5 horses and 12 pigs. In the dog, cat and horse, mm. levatores costarum are present from the second to the last rib. In the pig, these muscles are present from the second to the 15th rib, even in individuals with 16 pairs of ribs. Mm. levatores costarum longi and a levator of the first rib could not be found in the domestic animals although these muscles are described in man. All mm. levatores costarum are innervated by branches of the lateral branch of the ramus dorsalis of the respective thoracic nerve. An additional branch of the r. muscularis proximalis of the intercostal nerves 1-3 innervates the lateral part of the levator muscles of the second to the fourth rib.

The identification of the N τ-methyl histidine-containing dipeptide, balenine, in muscle extracts from various mammals and the chicken

1. 1. The occurrence of the dipeptide, balenine (β-alanyl-N τ-methyl histidine), has been identified by comparative chromatography in extracts of muscles from 9 species of mammal, including man, and the chicken. 2. 2. The identity of the dipeptide from 6 mammalian species and chicken was confirmed by preparative isolation prior to determination of the amino acid composition and N-terminal residue. 3. 3. In all cases, the dipeptide contained equimolar amounts of β-alanine and N τ-methyl histidine with β-alanine as the N-terminus. 4. 4. The concentration of the dipeptide varied dramatically between species, being just detectable in the muscle of man and rat while present at concentrations of up to 14 μmol/g wet muscle in adult pigs. 5. 5. It is proposed that balenine, like carnosine and anserine, should be regarded as a normal constituent of muscle.

Jaw-opening reflex activity in the inferior head of the lateral pterygoid muscle in man

Jaw-opening reflex excitation and inhibition in this muscle and the anterior digastric were only observed during activation and not when the muscles were relaxed. After electrical stimulation of the palate over the greater palatine nerve, reflex excitation of the lateral pterygoid was observed in all subjects with average latency 19.4 ms. Excitation in the anterior digastric muscle was found in only five of the eight subjects with latency 18.6 ms. Excitation of the jaw-opening muscles occurred during the inhibition of the jaw-closing muscles, and conversely, jaw-closing muscle excitation occurred during a silencing of the jaw-opening muscles. This suggests a central control over the facilitation and inhibition of jaw-opening and jaw-closing muscle activity.

Inhibition of muscular glucose uptake by lipid infusion in man

During a high-dose intravenous infusion of a mixed MCT/LCT-lipid emulsion and a conventional LCT-emulsion respectively, muscle substrate metabolism was investigated using the human forearm technique. With both lipid emulsions, a decrease in fractional muscular glucose extraction was seen, leading to significantly reduced muscular glucose uptake rates. An inverse linear relation between arterial tree fatty acids supply and fractional glucose extraction was seen suggesting that a mechanism according to Randle's glucose fatty acid concept is operating in skeletal muscle in man.

Correlation Between Intracavernous Pressure and Contraction of the Ischiocavernosus Muscle in Man

An artificial erection was induced in nine patients consulting for erectile dysfunction. Changes in the intracavernous pressure (ICP) and in the integrated EMG of the ischiocavernosus muscle were recorded during voluntary muscular contractions. During such contractions elevations in ICP, varying between 100 and 525mm. Hg, were recorded. Changes in ICP were always in phase with changes in the integrated electromyogram (EMG) of the ischiocavernosus muscle, and correlations between the duration of changes showed an almost perfect linear relationship between both physiological events. Correlations between maximum changes in ICP and integrated EMG generally showed a positive relationship between both measures. Results are interpreted to suggest involvement of the ischiocavernosus muscle in the process of penile rigidity.

Skeletal muscle lactate dehydrogenase isozyme alterations in men and women marathon runners.

Total lactate dehydrogenase (LD) and LD isozyme activities in gastrocnemius muscle from trained men and women runners were measured in response to the chronic stress of training for a marathon race (42.2 km). Following 9 wk of training, total LD activity in skeletal muscle from men and women runners significantly (P less than 0.02) decreased 2.26 and 2.25 U/mg protein, respectively. However, men's total LD activities were significantly (P less than 0.001) less than the women's both before and after training. Significant (P less than 0.05) increases in LD1 activities in skeletal muscle in men and women runners were also observed after training. No significant correlations were detected between percent fiber type composition in men or women vs. the changes in total LD activity, changes in LD1 activity, maximal O2 consumption or training distance averaged per week after the training period. The biochemical adaptations in skeletal muscle that occurred in the LD isozyme composition in both men and women runners make the runners skeletal muscle appear similar to heart muscle in LD1 and LD2 activities.

Physiological adaptation to physical conditioning. Old problems revisited.

Three classical problems in the field of man's adaptive response to exercise are reviewed. A case is made for the pump capacity of the heart limiting maximal oxygen uptake in man. This conclusion is based on findings that the capacity of skeletal muscle of man markedly surpasses that of the heart supplying it with a flow and thereby oxygen. It is suggested that only one third of the muscle mass of man can fully tax the capacity of the heart and consume the oxygen delivered by the heart. If a larger muscle mass is intensely engaged in the exercise, vasoconstriction must occur in the arterioles of the exercising limbs to avoid a reduction in blood pressure. Evidence is presented that a decrease in heart rate at submaximal exercise-observed after a period of physical conditioning, is caused by an altered autonomic chronotropic activity to heart, which most likely is due to a less potent feed back reflex from exercising muscles. The enlarged stroke volume is secondary to a larger diastolic filling, which via a Frank-Starling mechanism results in an elevation in the stroke volume. Last, it is argued that the altered metabolic response to exercise after physical conditioning, i.e. the larger lipid oxidation and reduced lactate production, results from local regulatory mechanisms rather than from changes in supply of oxygen, substrates, or hormones. Further, the muscle metabolic response to exercise is thought to play a major role in modulating systemic cardiovascular regulation in exercise.

The function of α- and β-adrenoceptors in isolated heart muscle of man

The function of α- and β-adrenoceptors in isolated heart muscle of man