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Biomedical subjects

R Le Bars

Publications and source records attributed to R Le Bars.

At least 19 recordsLinked to original sources
PubMed1990

Muscle fatigue unrelated to phosphocreatine and pH: an "in vivo" 31-P NMR spectroscopy study.

Metabolic events were followed by 31-P NMR spectroscopy during mechanical exhaustion of directly stimulated rat gastrocnemius. During mechanical fatigue, phosphocreatine (PCr) and pH first declined but although stimulation continued high values were recovered without mechanical recovery. Total recovery was only observed after cessation of stimulation. Partial mechanical recovery was elicited by lowering stimulation rhythm; it was accompanied by decrease in PCr to a steady-state level without pH alteration. When exhaustive exercise was induced immediately after nonexhaustive exercise, failure of mechanical function occurred without decrease in pH. Major findings were: first, during exhaustive stimulations, the greater the muscle fatigue, and the higher the PCr level at the end of stimulation. Secondly, PCr and force levels did not depend on preceding levels of PCr and pH. Thirdly, acidosis was observed transiently during the first minutes of the first exercise period. These findings strongly suggested that electrical events and/or excitation-contraction (EC) coupling play a crucial role in this type of fatigue.

Acidosis↗
PubMed1989

Phosphocreatine and pH recovery without restoration of mechanical function during prolonged activity of rat gastrocnemius muscle: an in vivo 31P NMR study.

Metabolic impairment in skeletal muscle was suggested to be involved in the development of local mechanical fatigue but until now results have dealt with short activity periods whereas little data on exhaustive and prolonged exercises are available. Stimulations of rat leg muscle lasting 45 min were induced by tetanic trains delivered via sciatic nerve at five different rhythms. Energy metabolism of the stimulated gastrocnemius muscle was followed by 31P NMR spectroscopy using surface coil while mechanical function was recorded. Our data showed a decrease in the force level to very low values a few minutes after exercise onset. This mechanical impairment only induced a transient metabolic failure followed by rapid restoration of high phosphocreatine (PCr) values and intracellular pH, without mechanical recovery. In addition, at the end of exercise, the PCr content was proportional to the fatigue level. As these experiments could not have impaired neuromuscular junction, the data would indicate that fatigue was maintained by a mechanism which does not appear to depend directly on muscle cell energy stores.

Adenosine Triphosphate↗
PubMed1986

[Modalities of the hyperventilation of exercise in maximal triangular effort on the ergometry bicycle in 11-to-13-year-old boys].

Tidal volume, respiratory frequency, ventilatory equivalent, mean inspiratory flow Vt/Ti, and respiratory timing Ti/Ttot were measured at each level of an incremental exercise in a group of 8 untrained boys. Breathing pattern of the child is characterized by a fast frequency and a small tidal volume. Ventilation at maximal exercise reaches 50% of adults mean value. For the same ventilation, Vt/Ti (when expressed in ml X mn-1 X kg-1) is higher in the child. That suggests a higher central inspiratory activity.

Adolescent↗
PubMed1983

Automatic classification of electromyographic signals.

The results of the application of classification methods to electromyograph signals of weak contractions in normal and myopathic subjects are described. Methods of pattern recognition, previously presented, allow the selection of representative motor unit action potentials. The analysis is done with ordinal qualitative variables obtained by identification of shape descriptive parameters (amplitude, duration, number of phases, number of extrema). From this analysis, characteristic classes for normality and myopathy appear, from which a diagnostic aid by assignment can be made.

Action Potentials↗
PubMed1979

[Modification of the Hoffmann reflex in function of athletic training (author's transl)].

The present study measures the values of the Hoffmann reflex and principally the relationship between the maximum reflex response and the maximum direct motor response (H max/M max) and their evolution. The subjects were athletes, performing aerobic and anaerobic type activities, divided into six groups (swimmers; soccer players; tennis players; sprinters; middle and long distance runners; and nonspecific athletes). The results show the average values of the H max/M max (53%) to be not different from those of nonathletes. When separated into aerobic and anaerobic groups, significant differences were found: the values are significantly inferior for subjects participating in anaerobic sports (37%) whereas we found an increase (from 55-75%) in the relationship for swimmers performing aerobic activities after 3 years of regular training. The results suggest, in accordance with previous authors, the possibility of a correlation between the modifications of the H max/M max and the type of activities (aerobic or anaerobic).

Female↗
PubMed1979

[A case of familial muscle weakness corrected by exercise (author's transl)].

The symptom described as muscle weakness corrected by exercise appears to be part of the recessive form of congenital myotonia, of which it can constitute the dominant clinical manifestation in some cases. This symptom coincides with decrements of the action of potentials to repetitive stimulations in the electromyogram, which may be particularly severe in these same cases. These observations contribute to the modification and precision of the description of the recessive form of Thomsen's disease, but their pathogenicity remains unclear.

Diagnosis, Differential↗