Biomedical subjects

B Maton

Publications and source records attributed to B Maton.

At least 55 records · Page 3Linked to original sources

PubMed1992

Masticatory muscle fatigue: endurance times and spectral changes in the electromyogram during the production of sustained bite forces.

The purpose of this experiment was to determine if the characteristics of fatigue observed in the limb muscle system are also evident in the muscles of mastication, specifically, the masseter and temporalis. Surface electrodes were placed bilaterally over the masseter and temporalis muscles of 10 adults. Each subject was instructed to maintain maximal and six levels of submaximal incisal bite forces for as long as possible. The power density spectrum of the electromyographic signals for each muscle was calculated at the onset and failure of the task. The decrease in endurance time with an increase in bite force followed a pattern similar to that in limb muscles, and each muscle was characterized by a consistent reduction in the mean power frequency of the power density spectrum and a variable change in r.m.s. power. The variability of changes in r.m.s. power (which is inconsistent with changes found in the limb muscles) was explained in terms of either changes in motor-unit firing rate or the muscle's relative contribution to the generation of bite force. The analyses also demonstrated a curvilinear relationship between bite force and r.m.s. power, but no relationship between bite force and the mean power frequency of the power density spectrum.

Adult↗

PubMed1992

Positive transfer of audiogenic kindling to electrical hippocampal kindling in rats.

Audiogenic seizures in genetically susceptible rodents are provoked by intense acoustic stimulations which result in a tonic seizure associated with a short flattening of the EEG. These seizures have been shown to involve primarily brainstem structures. Daily exposure to sound for 30-40 days produced a permanent change in the evoked seizure with development of facial myoclonias, rearing and falling, or of tonic-clonic seizures accompanied by high amplitude cortical spike-and-wave discharges. Kindled audiogenic seizures appear similar to seizures kindled from amygdala or hippocampus, suggesting that repeated auditory stimulations cause a progressive propagation of the epileptic discharge toward limbic structures. To verify this hypothesis, the behavioral and EEG development of electrical hippocampal kindling has been studied in 7 non epileptic controls (NE), 8 acoustic susceptible (AS), and 8 audiogenic kindled rats (KAS). The behavioral and EEG development of the electrical hippocampal kindling was similar in the AS and the NE rats. However, 2 animals in the AS group but no controls exhibited behavioral running and bouncing during the course of hippocampal kindling. In the KAS group, the hippocampal kindling was clearly facilitated as compared to NE and AS: behavioral stage greater than or equal to 5 was reached in a mean of 4 stimulations in KAS versus 30 and 22 stimulations respectively in NE and AS groups. This positive transfer phenomenon suggests that during kindling of audiogenic seizures, epileptic discharge spreads from the brainstem to the forebrain and progressively involves the hippocampus.

Acoustic Stimulation↗

PubMed1992

Continuous focal spikes during REM sleep in a case of acquired aphasia (Landau-Kleffner syndrome).

We report a girl 3 years and 6 months old with onset of aphasia at age 3 years and 3 months. There was no evidence of brain damage and there were no seizures. The neuropsychological evaluation showed that the girl tended to be right-handed, that aphasia was global and that other higher cortical functions seemed to be preserved. Isolated spikes and spikes-and-wave were recorded during wake over the right temporal region with rare independent contralateral abnormalities. During polysomnography (PSG), the physiological patterns of sleep were preserved and right temporal epileptiform discharges were significantly increased in all sleep stages. Maximal activation was obtained at sleep onset and during rapid eye movement (REM) sleep periods, when focal abnormalities became continuous and spread contralaterally. Repeat PSGs showed that the activation profile retained this particular trait, although subclinical discharges tended to increase during slow wave sleep (SWS). This pattern of subclinical temporal status epilepticus during REM sleep differs from the characteristic activation profile found in the syndrome of continuous spikes-and-waves during SWS. However, this profile was transient and all epileptiform changes disappeared during clinical recovery at 18 months of follow-up.

Anticonvulsants↗

PubMed1992

Evaluation of human dynamic contraction by phonomyography.

Phonomyogram (PMG, or acoustic myogram) is known to increase with force in isometric contractions. We investigated this relationship for dynamic contractions against different inertias. PMG and surface electromyogram (EMG) from biceps brachii and brachioradialis muscles were simultaneously recorded with the angular acceleration of elbow flexions. These were self-initiated movements (30 degrees) toward a fixed target and performed against two different inertias. PMG and EMG were integrated from the onset of the signal to the end of the acceleration phase. Phono- and electromechanical delays were also measured. For integrated EMG (iEMG), there was a linear relationship between integrated PMG (iPMG) and force, the slope of which did not depend on inertia. There was also a linear relationship between iPMG or iEMG and angular acceleration, with a higher slope for the highest inertia condition. There was also a family of linear relationships between iPMG or iEMG and angular acceleration, and their slopes depended on inertia. Measurements of the phono- and electromechanical delays showed that onset of PMG followed that of EMG but preceded onset of acceleration. It is suggested that PMG expresses tension of the underlying muscle contractile elements. Given the simplicity of the PMG method, we conclude that PMG allows convenient evaluation of muscle tension during human dynamic contraction.

Adult↗

PubMed1992

Electromyographic recording of the jaw reflex in Friedreich ataxia.

Jaw jerk was studied in 10 subjects with Friedreich ataxia, and 10 normal subjects for comparison. Electromyographic recording from the right masseter muscle showed a reflex response in all cases, in contrast to the absence of tendon reflexes in the four limbs for the ataxics. The mean latency of the jaw jerk was normal. These observations indicate that the jaw reflex arc is preserved, and that no damage to the trigeminal neuromuscular pathway exists for all the patients observed.

Adult↗

PubMed1991

Cortical post-spike facilitations in elbow muscles during isometric contraction.

Averaged responses of elbow muscles to action potentials of 37 single motor cortex cells were analyzed in two Macaca fascicularis monkeys during performance of a submaximal but high level isometric contraction. Post-spike facilitations (PSFs) of the rectified electromyographic activity (EMG) were frequently (72%) observed. They consisted of PSFs largely distributed in agonistic (biceps brachii and brachioradialis) and antagonistic (triceps brachii) muscles. Some post-spike inhibitions (7%) were also noted. As compared with distal muscles PSFs, most of the proximal PSFs were of lower amplitude, probably because of the higher level of the contractions. These PSFs were also of longer latency. The data indicate functional connectivity between motor cortical cells and proximal limb muscles. Cortical cells with oligosynaptic and even, for a few of them, with monosynaptic connections to the alpha-motoneurones may contribute to recruitment of motor units (MUs) involved in proximal limb muscle contraction.

Action Potentials↗

PubMed1991

An electromyographic study of an all-out exercise on a cycle ergometer.

The electromyograms of the vastus lateralis, the vastus medialis and the biceps femoris have been recorded with surface electrodes during an exhausting exercise on a Monark cycle ergometer, derived from the Wingate test (a 45 second all-out exercise against a braking force equal to 70 N) and during the velocity plateaus of submaximal exercises performed before this exhausting exercise on the same ergometer against the same resistance. This experiment has been carried out in order to study whether central fatigue occurs during an all-out anaerobic capacity test. One subject excepted (a former 800 m runner and road cyclist), there was a decrease in the electro expected integrated electromyogram (iEMG) during the exercise. The iEMG declines of the vastus medialis and the vastus lateralis were parallel and the revolution-to-revolution iEMG changes of the vastus medialis were positively correlated with those of the vastus medialis. These EMG changes suggest the occurrence of a central fatigue during this type of exercise. It was not possible to show a general trend for the effect of fatigue upon the EMG activity pattern of the biceps femoris because of large difference between subjects.

Adult↗

PubMed1990

Phonomyogram and electromyogram relationships with isometric force reinvestigated in man.

Contracting muscle generates sounds which can be recorded easily by means of a microphone. To determine if a phomomyogram (PMG) can be used to monitor muscle force, a comparison was made between simultaneous recordings of PMG and monopolar electromyogram (EMG) from the isometrically contracting biceps brachii muscle and the external flexion force. Locations of the monopolar electrode and microphone were identified in relation to the motor point. Whatever the recording site, PMG amplitude was proportional to EMG amplitude and both showed a quadratic relationship to muscle force. Changes in the PMG spectrum with force were similar to those in EMG, i.e. the mean power frequency increased up to about 30% maximal voluntary contraction and then reached a plateau. Despite a slightly higher variability, PMG was shown to be a valid index of muscular isometric force. At the same force, the amplitude of both PMG and EMG was lower in the prone than in the supine position of the hand. This result indicated a selective recording of biceps brachii muscle activity.

Adult↗

PubMed1989

The fatigability of two agonistic muscles in human isometric voluntary submaximal contraction: an EMG study. I. Assessment of muscular fatigue by means of surface EMG.

During an external isometric constant torque (25% of the maximal voluntary contraction) maintained until the maximal endurance time (limit time), we analysed and compared the changes in electromyographic (EMG) activity illustrating muscular fatigue simultaneously with mechanical activity (the tangential acceleration theta") related to physiological tremor. The EMG activities recorded were of two agonistic flexors, the biceps brachii (BB) and the brachioradialis (BR) muscles and one of the main extensors, the triceps brachii (TB). The integrated EMG increase and the mean power frequency (MPF) of the power spectrum density function (PSDF) decrease were larger for BR than for BB activity. These two findings suggested a greater BR fatigability. However, it is shown that differences between BB and BR MPF changes could be related to differences in the PSDF upper frequency limit of the two muscles and also to the relative magnitude of their tremor component.

Adult↗

PubMed1989

The fatigability of two agonistic muscles in human isometric voluntary submaximal contraction: an EMG study. II. Motor unit firing rate and recruitment.

The recruitment and firing rate of biceps brachii (BB) and brachioradialis (BR) motor units (MUs) were studied in the course of fatiguing isometric contractions at 20%-30% of maximal voluntary contraction (MVC). MU recruitment generally occurred throughout the maintained contraction and was similar for BB and BR muscles. Newly recruited MUs started to discharge in the form of bursts, the duration of which increased until a continuous rhythmical firing was achieved. Within each burst, the first interval between two consecutive discharges was usually the shortest. MU threshold was lowered just after the limit time of the maintained contraction. The MU's firing rate either increased or remained stable as a function of the elapsed time. It is concluded that (1) in fatiguing isometric contractions at 20%-30% MVC contractile failure is mainly compensated for by MU recruitment and a lowered MU threshold and (2) differences between in surface changes in the electromyogram of BB and BR muscles cannot easily be explained by related differences in MU firing rate and recruitment.

Adult↗

PubMed1989

Morphological and biochemical changes in old rat muscles: effect of increased use.

Male Wistar rats were strength and swim trained during a substantial period of old age to determine the influence of aging and activity on the histochemical and metabolic characteristics of a predominantly slow (soleus) and a predominantly fast (plantaris) skeletal muscle. Strength training counteracted the age-related atrophy of the fibers and the age-induced changes in fiber-type distribution of both muscles. Swim training, on the other hand, was without any effect on these parameters. The activity of both mitochondrial and cytoplasmic enzymes became lower with aging in the soleus muscle, whereas only the activity of the cytoplasmic enzymes became lower in the plantaris. Strength training reduced the aerobic capacity of both muscles, whereas swim training had the opposite effect. Aging induced a lower glycogen concentration of the lateral gastrocnemius muscle. This was avoided by swim training. The phosphocreatine and adenosine 5'-triphosphate concentrations were unchanged with aging but became higher with strength training. The activity pattern, therefore, seems to have a considerable influence on the age-related modification of the histochemical and metabolic characteristics of skeletal muscles of the rat. The effect, however, is related to the recruitment pattern of the fiber populations and the form of activity.

Adenosine Triphosphate↗

PubMed1988

In vivo muscular force analysis during the isometric flexion on a monkey's elbow.

An experimental method has been developed to analyse muscular forces and torques in vivo during isometric flexion of the elbow in small monkeys (Macaca fascicularis). A mini-transducer was built with a view to measure forces in situ, without cutting tendons. The positions of tendon insertions were measured on anatomical parts, then integrated in a series of calculations aiming of deducing the lever arms of forces to be included in a torque equilibrium relationship. Muscle activity of the three main flexors was measured for five angles of isometric flexion between 70 degrees and 110 degrees, 0 degrees corresponding to the full extended forearm. The analysed signals were selected using physiological and biomechanical criteria. Then, results corresponding to force participation, and torque participations, were worked out; they are presented and discussed in the present paper.

Animals↗

PubMed1988

Myoelectrical and mechanical changes linked to length specificity during isometric training.

Mechanical and neural activation changes that accompanied muscle isometric training were studied in males. Training and testing sessions consisted of right elbow isometric flexions. Each experimental group was trained during 5 wk at one of the following angles: 25, 80, and 120 degrees. Bipolar surface electromyogram (EMG) was recorded from the biceps brachii and brachioradialis muscles. An improvement of maximal voluntary contraction (MVC) was always found at the training angle and was systematically greater than at the other angles. Moreover, the shorter the muscle length at which the training has been carried out, the more the gain was limited to the training angle. An increase of the maximal integrated EMG of both biceps brachii and brachioradialis frequently accompanied the improvement of MVC at the training angle.

Adult↗

PubMed1987

Relationships between individual isometric muscle forces, EMG activity and joint torque in monkeys.

The aim of the present work was to determine the EMG activity and the moment of force developed by the main elbow flexor muscles, and to establish on this basis the degree of their participation in isometric contractions performed at various positions of the elbow. This was achieved by recording the following biomechanical parameters: EMG and tensile stress (or force) from biceps brachii (BB) and brachioradialis (BR); EMG from brachialis; external resultant force (FE). There was: a linear or quadratic relationship between the integrated EMG from each muscle and FE; a linear relationship between the force produced by BB or BR and FE. The slope of these relationships depended on the elbow angle, except for that between BB force and FE. It is proposed that iEMG changes compensate for those of the force lever arm. It has been calculated that the contribution of BR to external torque decreased from the extension to flexion while that of BB increased from 70 degrees to 90 degrees and then decreased. How far these data can be extrapolated to man is a matter of discussion based on iEMG and anthropometrical data.

Animals↗

PubMed1987

Differences between motor unit firing rate, twitch characteristics and fibre type composition in an agonistic muscle group in man.

A comparison was carried out between the motor unit (MU) firing rate and the characteristics of the twitch and the fibre type composition of anconeus and triceps brachii. Fibre type composition (type I, type II) was determined in whole cross-sections of cadaver specimens. The proportion of type I fibre was 60%-67% in anconeus and 32-40% in the lateral head of triceps brachii. Reflecting these histochemical differences, the contraction time of anconeus and triceps was 92 +/- 9 ms and 68 +/- 9 ms respectively. It follows that anconeus can be classified as a slow muscle, as opposed to the lateral head of triceps. The relationship between MU firing rate and isometric force, tested at 90 degrees elbow flexion, differed between the two muscles for force values below 30% of maximal voluntary contraction. No significant increase in MU firing rate was found in anconeus at forces above 5% of maximal voluntary contraction. It is concluded that even within a single agonistic muscle group acting at a single joint there is an adaptation of MU firing rate to the contractile characteristics of each muscle.

Arm↗

PubMed1987

Modulation of slow and fast elbow extensor EMG tonic activity by stretch reflexes in man.

Reflex EMG responses to sudden passive flexion of the elbow were recorded from anconeus and triceps brachii in 5 human volunteers. While the subjects were required not to resist the flexion movement, they were required to maintain an extension torque of 3.5 or 7.0 Nm prior to its onset. Under these isotonic conditions, the latency and amplitude of the reflex activities from anconeus and triceps brachii did not differ significantly, in contrast to the findings of Le Bozec (1986) in actively relaxed subjects. The myotatic/postmyotatic EMG amplitude ratio did not provide a further quantitative way to distinguish between these muscles. The absence of a difference between the reflex activities of a slow (anconeus) and a fast (triceps brachii) muscle is interpreted as resulting from a strong drive of spindle activity on the whole extensor motoneuron pool, which outweights the differences in recruitment due to the differing relative amounts of type I and type II fibres in the two muscles. Differences like those described between finger and calf muscles by other authors are thought to be due to the relative degree of corticalization of these muscles. All short and long latency responses of the muscles increased in magnitude and decreased in latency with increasing background EMG activity as well as with increasing initial length. The position and tonic activity dependency of these responses is explained in terms of alpha-gamma coactivation.

Adult↗

PubMed1987

Long-latency stretch reflexes of the human elbow extensors during voluntary relaxation: differences between agonistic muscles.

Reflex electromyographic (EMG) responses of elbow extensor muscles to unexpected elbow flexion were recorded in the absence of initial tonic activity from subjects instructed not to resist the stretch. The monosynaptic component M1 was present only in the anconeus muscle and only for high accelerations. The acceleration value at which the long-latency components M2 and M3 appeared was lower for anconeus than for triceps brachii. Increases in peak acceleration of stretch resulted in decreases in M2 and M3 latencies and increases in M2 and M3 magnitudes in both muscles. However, M2 and M3 latencies for anconeus were shorter than those of triceps brachii, except at high acceleration values. Furthermore, the magnitude of M2 and M3 components of anconeus activity increased faster for low accelerations than for high accelerations, whereas those of triceps brachii increased in proportion to the acceleration. These differences between anconeus and triceps brachii were similar to those described earlier for voluntary movements. It is suggested that the motoneurons of all elbow extensor muscles may be recruited as a single motoneuron pool following Henneman's size principle, irrespective of whether the activity is voluntary or reflex in origin.

Adult↗

PubMed1985

The flexor function of the m. pronator teres in man: a quantitative electromyographic study.

The muscle pronator teres was studied by surface electromyography during elbow flexion in a horizontal plane. The forearm was in semi-pronation and movement was performed at various velocities. A quantitative comparison was made between pronator teres activity and two main elbow flexors, biceps brachii and brachioradialis. The mean timing of the onset of activity was constant: biceps brachii was activated first followed by pronator teres and brachioradialis, and the lower the velocity of flexion, the earlier was the onset of biceps brachii activity. There was a linear relationship between the integrated EMG from each muscle and the work done. However, this relationship was less exact for pronator teres and brachioradialis at low values of work, a finding which opens questions about the generality of this relationship and about the "muscle equivalent" concept. Pronator teres appears to participate in elbow flexion besides its role in pronation. Despite similar anatomical peculiarities, pronator teres does not behave in the same way as anconaeus or popliteus and, above all, it is not the sole muscle active in slow movement. Thus, all the stocky muscles lying close to an articulation do not behave in the same way.

Adult↗