Les effets métaboliques de l'exercice

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Improving health status through physical activity for individuals with chronic pulmonary diseases

International audienceThe aim of this paper is to show how pertinent pathophysiological bases have been built for physical activity prescription for individuals with obstructive pulmonary disease (asthma and chronic obstructive pulmonary disease). The pathophysiological bases were constructed by taking into account exercise mismatching, which was analyzed in terms of both short- and long-term impact on disease outcome. Specific exercise adaptations based on a keen understanding of the underlying physiological processes provided the key to an adapted intervention with well-defined exercise program aims. The results that were achieved are striking, and one might conclude that sometimes exercise is simply the best way to improve the general well-being of individuals with chronic disease. Since this is a major concern for health professionals and chronically ill individuals, physical activity offers a means to rise to this challenge

Les effets métaboliques de l'exercice

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Question 3-6. Les questionnaires d’activité physique - application aux BPCO

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What is known about fatigue sites under neuromuscular electrical stimulation?

International audienceFatigue is a complex phenomenon involving different mechanisms (central and peripheral). The study of fatigue under neuromuscular electrical stimulation (NMES) has been ignored for a long time, due to the assumption that since NMES is applied over the peripheral level of the neuromuscular system, it cannot implicate central nervous system reactions. However, several arguments in the literature point to a real implication of central structures during NMES. This led to the study of the electrically induced fatigue and results show that supra-spinal fatigue is developed after both high- and low-frequency stimulation, further proving the non-purely peripheral character of this technique

Neuromuscular Fatigue Is Not Different between Constant and Variable Frequency Stimulation

International audienceThis study compared fatigue development of the triceps surae induced by two electrical stimulation protocols composed of constant and variable frequency trains (CFTs, VFTs, 450 trains, 30 Hz, 167 ms ON, 500 ms OFF and 146 ms ON, 500 ms OFF respectively). For the VFTs protocol a doublet (100 Hz) was used at the beginning of each train. The intensity used evoked 30% of a maximal voluntary contraction (MVC) and was defined using CFTs. Neuromuscular tests were performed before and after each protocol. Changes in excitation-contraction coupling were assessed by analysing the M-wave [at rest (M-max) and during MVC (M-sup)] and associated peak twitch (Pt). H-reflex [at rest (H-max) and during MVC (H-sup)] and the motor evoked potential (MEP) during MVC were studied to assess spinal and corticospinal excitability of the soleus muscle. MVC decrease was similar between the protocols (28%, P<0.05). M-max, M-sup and Pt decreased after both protocols (P<0.01). H-max/M-max was decreased (P<0.05), whereas H-sup/M-sup and MEP/M-sup remained unchanged after both protocols. The results indicate that CFTs and VFTs gave rise to equivalent neuromuscular fatigue. This fatigue resulted from alterations taking place at the muscular level. The finding that cortical and spinal excitability remained unchanged during MVC indicates that spinal and/or supraspinal mechanisms were activated to compensate for the loss of spinal excitability at rest

Neuromuscular fatigue during triceps surae low-frequency electrical stimulation in subjects with different force generating capacity

International audienceFatigue induced by neuromuscular electrical stimulation (NMES) is poorly understood. Although recent research gives evidence for the implication of different sites along the pathway of force production, the muscle factors susceptible to influence the response to electrically induced fatigue are still unknown. The purpose of the present study was to identify the time course of neuromuscular changes during NMES according to the muscle's capacity to generate force. Twelve healthy subjects with different force generating capacities [7 Strong (S) with mean torque during Maximal Voluntary Contraction (MVC) 88.8±1.6Nm and 5 Weak (W) with mean torque 64.4±3.2Nm], participated in an electrostimulation protocol for the triceps surae, composed of 3 series of 17 stimulation trains (4s ON - 6s OFF, pulse duration 450μs, frequency 30Hz, at maximal tolerated intensity). Neuromuscular tests were performed before, during and immediately after the protocol. Torque and EMG activity of the gastrocnemius medialis muscle were continuously recorded. Alterations in muscle's characteristics (excitability and contractile properties) were evaluated by analysis of the muscle compound action potential (M-wave) and twitch torque. Motoneuron excitability was assessed by the H reflex, expressed in absolute value and normalized to M-wave maximal amplitude (respectively Hmax and H/M). Changes in the central command were assessed by using the twitch interpolation technique and the root mean square (RMS and RMS/M) obtained during MVC. MVC significantly decreased from the first 17-train bout and throughout the protocol for both groups (from 88.8±1.6Nm vs 64.4±3.2Nm at pre to 78.8±3.3Nm vs 58.2±2.7 at post51, for S and W respectively), giving evidence of precocious neuromuscular impairments. Motoneuron excitability was not affected (no change of Hmax and H/M). Muscle contractile properties were significantly potentiated at post17 and for the rest of the protocol (42±14% for S vs 37±6% for W for Pt values at post51) for both groups. Muscle excitability was significantly altered only in S, as proved by the significant decrease in M-wave amplitude and muscle response to trains of stimulation (-2.9±3.7% and -13.4±5.9% for post51 respectively). Level of voluntary activation assessed by the twitch interpolation technique was lower for W and, although RMS/M was significantly decreased for both groups, the decrease in W was significantly more pronounced (-21.8±4.5% vs -14.5±6.2% for S). Neuromuscular fatigue can be attributed to both central and peripheral mechanisms for the S group, while for W it appears that mainly central mechanisms are involved. These observations should be taken under consideration when seeking to optimise training strategies for people with neurological disorders. The results show that improving muscle strength does not necessarily delay neuromuscular fatigue, but does change its nature

Anomalies métaboliques du patient infecté par le Virus de l'immunodéficience humaine (VIH) sous multithérapie antirétrovirale (vers une individualisation de la prise en charge par l'entraînement aérobie)

MONTPELLIER-BU Médecine UPM (341722108) / SudocMONTPELLIER-BU STAPS (341722109) / SudocMONTPELLIER-BU Médecine (341722104) / SudocSudocFranceF

Does Central Fatigue Exist Under Low-Frequency Stimulation of a Low Fatigue-Resistant Muscle ?

International audienceThe aim of the present study was to determine whether central fatigue occurs when fatigue is electrically induced in the abductor pollicis brevis muscle. Three series of 17 trains (30 Hz, 450 ls, 4 s on/6 s off, at the maximal tolerated intensity) were used to fatigue the muscle. Neuromuscular tests consisting of electrically evoked and voluntary contractions were performed before and after every 17-train series. Both the force induced by the stimulation trains and maximal voluntary force generation capacity significantly decreased throughout the protocol (-27 and -20%, respectively, at the end of the protocol, P\0.001). These decreases were accompanied by failure in muscle excitability (P\0.01), as assessed by the muscle compound action potential (M-wave or Mmax), leading to significant impairment in the muscle contractile properties (P\0.05), as assessed by the muscle mechanical response (Pt). Central fatigue indices (level of activation, RMS/ Mmax and H reflex) were not significantly changed at any point in the protocol. This gives evidence of preserved motor command reaching the motor neurons and preserved spinal excitability. The results indicate that this low-frequency stimulation protocol entails purely peripheral fatigue development when applied to a low fatigue-resistant muscl