No description available.

Spinal cord injury is a devastating neurological disorder partially characterized by a loss of motor function below the lesion. The dramatic loss of activity results in muscle atrophy and slow-to-fast transformation of contractile elements, producing smaller, weaker and more fatiguable muscles. Functional electrical stimulation (FES), has been proposed in order to induce muscular activity and reverse these changes. FES has primarily been applied in the periphery, either at the surface or implanted in or around a nerve or muscle. Although this can excite nervous tissue and produce muscular contractions, these systems often produce reversed recruitment of motor units leading to inappropriate force generation and increased fatigue. We applied intraspinal microstimulation (ISMS) through fine microwires implanted into the spinal cord of rats. Electrical stimulation through these microwires caused contractions of the quadriceps muscles in both acute and chronically spinalized animals. We showed that muscle recruitment is significantly more gradual with ISMS in intact rats compared to that produced by a standard nerve cuff. Our results further showed that this was due to preferential activation of fatigue resistant muscle fibers. Given this more orderly recruitment of motor units by ISMS, we tested the muscle phenotypes produced by ISMS or nerve cuffs after chronic stimulation. Surprisingly, over a 30 day stimulation period the quadriceps muscles chronically activated by either daily ISMS or nerve cuff stimulation underwent similar fast-to-slow transformations in fiber type and functional properties. This indicates that the recruitment order of motor units does not play the only role in determining the muscle phenotype. Other factors such as the total daily time of activity may be critically important to the phenotypic outcome of skeletal muscle. Finally, we demonstrated that quadriceps force recruitment by ISMS was unchanged following the 30 day stimulation period. In addition, 30 days of chronic ISMS did not cause observable damage in the spinal cord beyond that incurred by the implantation of sham microwires. These studies advance our understanding of the force recruitment properties, neuromuscular plasticity and damage incurred by ISMS and move us closer to developing a clinically viable ISMS procedure.

No description available.

Electric muscle stimulation (EMS) has been widely used in the rehabilitation of musculoskeletal injuries. Patterned electrical neuromuscular stimulation (PENS), a specific form of EMS, has been developed to better educate muscles to contract properly. The physiological efficacy of PENS has not been quantifiably identified. OBJECTIVES: The aim of this study is to determine the acute effect of one PENS training session (3 sets of 10 1-sec repetitions) on maximal isometric knee extensor (MVIC) torque production and surface EMG (sEMG) in healthy nonathlete college students. DESIGN: A randomized repeated-measures design was used in this study. METHODS: Twenty-two male college students participated in the study. All participants completed two training sessions, one with PENS and one without, in a randomized crossover design. RESULTS: One bout of PENS training significantly increased MVIC (3.1% ± 1.7%, p = 0.03) which was greater than the change in MVIC of the control group (p = 0.03). Control training did not alter MVIC but resulted in significant decrease in average sEMG amplitude (-7.8% ± 1.6%, p ≤ 0.01) and peak sEMG amplitude (-10.4% ± 2.7%, p ≤ 0.01). These reductions in sEMG following control training were significantly different from the PENS group (p = 0.03 and p ≤ 0.01). CONCLUSIONS: The findings suggest that strength training in conjunction with PENS can enhance torque production after just one bout of training. The increase in torque with no change in sEMG amplitude can be explained by increased motor unit synchronization or decreased cocontraction of antagonist muscles.

No description available.

L'ectrostimulation dite conventionnelle (CONV) est délivrée par des impulsions électriques de basse fréquence (≤ 50 Hz), de courte durée (< 400 μs) et de haute intensité. Ce type d'ESNM permet ainsi d'évoquer une contraction musculaire grâce à l'activation directe des axones moteurs et est associé à une fatigue musculaire exagérée par rapport aux contractions volontaires (VOL). Au contraire, lors de l'utilisation d'impulsions de longues durées (1 ms), de hautes fréquences (≥ 80 Hz) et de faibles intensités (i.e. protocole « Wide-Pulse, High-Frequency » (WPHF)), une partie de la force musculaire évoquée aurait pour origine des mécanismes centraux. En effet, une augmentation de la force produite en réponse à WPHF a été rapportée alors que l'intensité de stimulation était constante. Cette « extra force » (EF) refléterait le recrutement par voie réflexe des motoneurones spinaux. L'objectif de ce travail de thèse était de mieux appréhender les mécanismes neurophysiologiques à l'origine de l'EF et d'évaluer les conséquences métaboliques et corticales du protocole WPHF (1 ms - 100 Hz) par rapport à des protocoles d'exercices VOL et de type CONV (50 μs - 25 Hz). Les réponses musculaires des fléchisseurs plantaires et les réponses cérébrales ont été évalué par résonance magnétique nucléaire (la spectroscopie par résonance magnétique du phosphore 31 du muscle et l'imagerie par résonance magnétique fonctionnelle du cerveau) et électrophysiologie (EMG). Ces résultats constituent une première étape importante vers une meilleure prise en charge des pathologies liées à des atteintes du neuromusculaire. / Conventional neuromuscular electrical stimulation (CONV) is delivered via surface electrodes at short pulse duration (< 400 μs), low frequencies (≤ 50 Hz) and high current intensities. The motor unit recruitment pattern of CONV, however, is different from the pattern of voluntary contractions (VOL) and leads to a hastened onset of muscle fatigue. The use of wide-pulses (1ms), high frequencies (100 Hz) (WPHF) and low current intensities might approach the natural activation pattern of VOL by enhancing the neural contribution to force production. Previous studies investigating WPHF reported progressive and unexpected force increments ("Extra Forces") despite a constant stimulation intensity which might reflect the more pronounced activation of sensory pathways within the central nervous system. The objective of this thesis was to investigate this "Extra Force" (EF) phenomenon and to evaluate the efficiency of WPHF (1 ms pulse duration at 100 Hz) in terms of metabolic demand and neural contribution to force production in comparison to CONV NMES (0.05 ms pulse duration at 25 Hz) and VOL. Our experiments comprised electrophysiological (EMG) and nuclear magnetic resonance techniques (31P spectroscopy of the muscle, functional imaging of the brain). The findings should be considered in future studies investigating the potential of NMES in a clinical context as a treatment for neuromuscular pathologies.