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Biomedical subjects

B Maton

Publications and source records attributed to B Maton.

At least 73 records · Page 4Linked to original sources
PubMed1983

Evolution of myoelectrical and precentral cell activities during learning of a new amplitude of movement.

The object of these experiments was to determine if changes in precentral neuron activity may be related to learning of a new amplitude of movement. Data were obtained from two monkeys trained to stop, in a given position, an elbow flexion movement in order to get a reward. A screen prevented the animal from seeing its forearm. The terminal position was not indicated by a cue, and movements were self-initiated. Motor performance and cell activity were analyzed during the period of learning of a new amplitude of movement. The cells studied presented the reciprocal patterns of activity: they were active flexion but discharged during passive extension. Results clearly indicated that: (1) amplitude was the actual parameter which was learned; (2) the peak frequency of discharge of motor cortex neurons increased during learning, as did the frequency of reward; and (3) the peak frequency of discharge related to passive movements was not changed by conditioning. The results support the hypothesis that the increase of the activity tied to active movements which is observed during conditioning may not be related to an increase of peripheral feedback but expresses a greater 'corticalization' of the movement.

Animals↗
PubMed1981

Human motor unit activity during the onset of muscle fatigue in submaximal isometric isotonic contraction.

The onset of fatigue has been studied by relating motor unit activity and surface myoelectric activity during constant force isometric contraction in man. The surface (global) EMG of the biceps brachii was recorded using bipolar electrodes. The global EMGs of the other elbow flexors were also recorded. Motor unit activity was recorded simultaneously at three points of the biceps brachii by using wire electrodes. The time course of the integrated surface EMG showed that fatigue occurred right at the beginning of the contraction. The increase of the integrated EMG was especially important when the value of the force maintenance was high. The time course of this increase was close to that of the output of the spikes recorded by the wire electrodes. No matter what the value of the force maintenance, MU recruitment occurred throughout the contraction. The existence of an increase in the MU firing frequently depended on the value of this force. Contractile element fatigue is believed to provide the explanation of these results, while neuromuscular junction fatigue may perhaps be more important near the time limit.

Action Potentials↗
PubMed1980

Fast and slow motor units: their recruitment for tonic and phasic contraction in normal man.

Most skeletal muscles include at least two types of MU's. Then, it has been stated that the properties of each MU may imply its specific recruitment in static or dynamic work. To test this hypothesis, the activities of biceps brachii MU's have been recorded during voluntary static contraction followed without any break by dynamic contraction. The MU's activity was recorded by means of wire-electrodes. From 45 tests carried out on 15 normal subjects in which 78 MU's were studied it has been found that: (1) the same MU may discharge both in static and in dynamic work; (2) in both types of work the MU's firing rate and recruitment only depend on the external force. For example, a single MU which does not discharge for a given level of static force will discharge during the following dynamic work, but can also be recruited for a higher level of static force. Thus, it can be said that the qualification "tonic" and "phasic", characterize the MU's twitches and do not imply any static-dynamic differentiation. A comparison has been made between the patterns of MU activity which occur in movement against load and those which have been found in movement against inertia. It is suggested that while the latter are preprogrammed, the former fall under a feed-back control.

Action Potentials↗
PubMed1980

The synergy of elbow extensor muscles during dynamic work in man. I. Elbow extension.

This study concerns the synergy of the elbow extensor muscles during voluntary elbow extension performed at various velocities against different intertia and in a horizontal plane. The quantity of excitation (Q) of the three heads of the triceps brachii muscle increases linearly with the external work (W). On the contrary, the anconeus Q increases rapidly for low values of W while for higher values it increases very slowly but linearly with the W. These results imply a proportionality between Q and W of the different muscles except in the case of anconeus for low values of W. Furthermore, it is shown that the position of the shoulder does not influence the relative contribution of the different muscles to W but leads to an adjustment of the activity of the long head. The different extensor muscles do not come into play simultaneously. The chronology of the muscular activities depends on velocity and inertia. The importance of anconeus activity for slow movements is pointed out, and it is suggested that there exists a specific control of the motoneurons of the different elbow extensor muscles. The limits of the concept of muscle equivalent are also discussed.

Adolescent↗
PubMed1980

The synergy of elbow extensor muscles during dynamic work in man. II. Braking of elbow flexion.

The muscular synergy between the elbow extensors was studied during the braking of voluntary elbow flexion performed in a horizontal plane at various velocities and inertias. The braking of movements performed at very low velocity is effected by passive viscoelastic forces. For higher velocities there exists a chronology of muscular activities which depends on both velocity and inertia. From the characteristics of this muscular chronology it is inferred that: 1. The anconeus plays an important role in braking slow movements. 2. The motor output is distributed separately to the motoneurons of each muscle. The muscular activity patterns are of three distinct types. The agonist-antagonist timing is correlated with velocity and inertia. Its dependence on reciprocal inhibition mechanisms is discussed.

Adult↗
PubMed1979

[The recruitment of motor units during elbow flexions in man].

The density of spikes of spike output (SO) recorded by means of three bifilar semimicroelectrodes simultaneously implanted in the biceps brachii has been studied during elbow flexions performed against inertia and with a variable velocity (anisometric, anisotonic contractions). The total number of motor unit (MU) potentials as well as the force were sequentially measured during intervals of 30 msec. SO obtained during movements of very similar mechanical characteristics was different from one movement to another. However, when a small number of identical movements was summed an averaged SO was obtained that was representative of the instantaneous global activity of the biceps. Taking into account the respective values of the bin duration and of the interval between two successive discharges of a single MU, the averaged SO represents the number of active MU during the acceleration phase of the movement. Since in this type of movement the frequency discharge of each MU decreases during the acceleration phase, it appears that the increase of averaged SO represents the recruitment of MU during the movement. From the relation established between the instantaneous values of So and force it can be concluded that the shape of force increase in anisometric, anisotonic conditions is entirely related to that of MU recruitment, although the absolute value of force depends on both the firing frequency and the number of active MUs.

Action Potentials↗
PubMed1977

The stability of synergy in agonists during the execution of a simple voluntary movement.

The characteristics of muscular synergy between the main elbow flexors (biceps brachii, brachialis, brachoradialis were considered. The activities of these different muscles were recorded simultaneously with surface and wire electrodes. A quantitative analysis of the activity of each of these muscles and of their excitation levels was carried out during movements performed at various velocities and against different inertias. It was shown that: (1) the onset as well as the cessation of activity in the different muscles occur practically simultaneously and independently of the velocity and inertia of the movement; (2) the well-known linear relation between the integrated EMG of biceps brachii and the work can be extended to the other main flexors. This implies that the relation between the activities of the main flexors remains constant whatever the velocity and inertia may be. These results confirm the notion of 'Flexor Equivalent'. They also demonstrate a stability of the synergy between agonist muscles which must be distinguished particularly from the synergy between agonists and antagonists.

Adult↗
PubMed1977

[Biceps brachii motor unit frequency and recruitment during static work (author's transl)].

The recruitment and the changes in firing frequency of biceps brachii motor units (MU) were studied during static work in normal man. The activity of single MUs have been followed from minimal to maximal levels of force, using three selective wire-electrodes inserted in the muscle. 1. The increase of MUs firing rate contributes to the force increase during the whole of the range of forces. However, the contribution of increased firing rate is more important at low force levels. 2. The firing rate variability is more important for low levels of force. This may be one of the mechanisms by which the summation of the twitches leads to a stable contraction. 3. At each level of force, the diverse MUs fire at the same mean frequency, except during the "catching up phase" which follows the start of the 'MUS activity. 4. The force generated by the muscle varies linearly with the number of active MUs, i.e. the MU recruitment has a constant contribution to the increase of force. 5. The comparison between firing rate and MU recruitment suggests that the first mechanism is more important f or low levels of force, while MU recruitment becomes more important at higher force levels.

Arm↗
PubMed1976

Motor unit differentiation and integrated surface EMG in voluntary isometric contraction.

The role of the differentiation of motor units (MU's) in the relation between integrated surface electromydgram and force was studied here for the biceps brachii, in the course of static contraction in man. The global EMG of the biceps brachii was recorded by two silver electrodes fixed to the skin. The MU's activity was simultaneously lead off by three bipolar wire electrodes inserted in three points of the muscle. MU firing frequency and recruitment were estimated by counting the action potentials on the three elementary records. The comparison between the increase of the integrated surface EMG and MU recruitment as a function of force shows that MU recruitment in itself cannot account for the increase in the integrated global EMG, particularly for high values of force. The difference between MU recruitmentand integrated global EMG, which can neither come from a possible MU's synchronisation as was shown in the discussion, is being suggested to be connected to the progressive firing of "phasic" MU's. This type of recruitment may also play an important role in the gradation of isometric force in normal man.

Action Potentials↗
PubMed1975

Motor unit activity and preprogramming of movement in man.

The activity of single motor units (MUs) is studied during voluntary dynamic movements in man. It is shown that as soon as a MU is set into activity, i.e., at the beginning of the myoelectric burst which precedes the start of the limb movement, there exists a consistent relationship between the peak velocity (for a given inertia) had the interval between the first two consecutive discharges of this MU. Thus, it is likely that when the amplitude of the movement is voluntarily limited, the peak velocity of the movement is preprogrammed.

Elbow Joint↗
PubMed1975

[Influence of the electrical properties of electrodes (platinum wire) on the myoelectric signal].

The use, in electromyography, of platinum wire electrodes required a knowledge of the electrical characteristics of these electrodes in the frequency range of the myoelectric signal. For this purpose the impedance of these electrodes was measured by the "cercle pointe" method (Gougerot 1951) in conditions similar to those in use. These electrodes behave like the majority of metal electrodes. Their impedance in particular can be represented by a polarization capacity shunted by an ohmic resistance, in series with a resistance representing the electrolyte resistance. It is shown that, depending on the electrode area and the way they are used, these electrodes can detect the myoelectric signals more or less selectively.

Electrodes↗