Changes in the distribution of muscle activity when using a passive trunk exoskeleton depend on the type of working task: A high-density surface EMG study.

Exoskeleton effectiveness in reducing muscle efforts has been usually assessed from surface electromyograms (EMGs) collected locally. It has been demonstrated, however, muscle activity redistributes within the low back muscles during static and dynamic contractions, suggesting the need of detecting surface EMGs from a large muscle region to reliably investigate changes in global muscle activation. This study used high-density surface EMG to assess the effects of a passive trunk exoskeleton on the distribution of low back muscles' activity during different working tasks. Ten, male volunteers performed a static and a dynamic task with and without the exoskeleton. Multiple EMGs were sampled bilaterally from the lumbar erector spinae muscles while the hip and knee angles were measured unilaterally. Key results revealed for the static task exoskeleton led to a decrease in the average root mean square (RMS) amplitude (∼10%) concomitantly with a stable mean frequency and a redistribution of muscle activity (∼0.5 cm) in the caudal direction toward the end of the task. For the dynamic task, the exoskeleton reduced the RMS amplitude (∼5%) at the beginning of the task and the variability in the muscle activity distribution during the task. Moreover, a reduced range of motion in the lower limb was observed when using the exoskeleton during the dynamic task. Current results support the notion the passive exoskeleton has the potential to alleviate muscular loading at low back level especially for the static task.

Does the amplitude of biceps brachii M waves increase similarly in both limbs during staircase, electrically elicited contractions?

OBJECTIVE: Humans usually tend to control more finely muscle force production in dominant than non-dominant upper limbs. It is well established that motor unit recruitment is a key mechanism by which muscle force is controlled, and we hypothesized that a relatively smaller number of motor units may be recruited in muscles of dominant than non-dominant limbs for any given increase in synaptic input. Hence, we investigated peripheral properties of dominant and non-dominant biceps brachii through the analysis of M-wave responses to incremental electrical stimulation. APPROACH: Current pulses at progressively greater intensities were applied in the proximal region of biceps brachii of 16 subjects while surface electromyograms were recorded with a grid of electrodes in the distal region. M-wave amplitude was averaged across channels and normalized with respect to the maximum amplitude value, separately for each stimulation intensity and limb. Amplitude-current intensity curves were interpolated to provide an equal number of stimulation levels between limbs. Differences between dominant and non-dominant arms were assessed through the average increase in M-wave amplitude for consecutive stimulation intensities (increments). MAIN RESULTS: Wilcoxon's signed-rank test showed that increments in the M-wave amplitude were significantly smaller (p = 0.017) in dominant than non-dominant biceps brachii. SIGNIFICANCE: The results suggest that there was a more gradual recruitment of motor units in biceps brachii of dominant than non-dominant arms. This is in agreement with the hypothesis of a broader spectrum of motor unit recruitment thresholds in the dominant arm, which may contribute to a finer regulation of force production.

Efeitos da estimulação elétrica funcional nos músculos do punho e dedos em indivíduos hemiparéticos: uma revisão sistemática da literatura / Effects of functional electrical stimulation applied to the wrist and finger muscles of hemiparetic subjects: a systematic review of the literature

CONTEXTUALIZAÇÃO: Faz-se necessária sistematização das evidências disponíveis sobre os efeitos da estimulação elétrica em pacientes hemiplégicos após o acidente vascular cerebral. OBJETIVO: Realizar uma revisão sistemática da literatura referente aos efeitos da eletroestimulação funcional para os músculos do punho e dedos de pacientes hemiplégicos adultos. MÉTODOS: Uma busca foi realizada nas bases de dados Medline, Lilacs e PEDro, no período de fevereiro a março de 2006, por trabalhos que documentassem os efeitos da intervenção nas características neuromusculares, musculoesqueléticas e funcionais. Dados foram extraídos de forma padronizada de cada estudo, e a qualidade metodológica foi avaliada utilizando-se a escala PEDro. RESULTADOS: Oito estudos aleatorizados foram revisados. Em relação à avaliação da qualidade da evidência dos trabalhos, as pontuações variaram entre 3/10 e 7/10 na escala PEDro. Apesar da diversidade de protocolos, características de participantes e instrumentos utilizados terem impedido o agrupamento dos resultados, a síntese em níveis de evidência demonstrou que há forte evidência de efeitos positivos da eletroestimulação na força muscular, tônus, função motora e uso do membro na rotina diária. Há evidência moderada para efeitos na destreza e evidência limitada para efeitos na coordenação motora e independência em atividades de autocuidado. Não há evidências para ganhos na amplitude de extensão ativa de punho. CONCLUSÃO: Apesar de apresentarem limitações metodológicas, estudos aleatorizados relatam efeitos positivos do uso da eletroestimulação no punho e dedos, o que sugere que essa terapia seja eficaz para a promoção de função do membro superior afetado de indivíduos hemiplégicos.

BACKGROUND: a systematization of the available evidence regarding the effects of electrical stimulation for hemiplegic patients following stroke is needed. OBJECTIVE: to conduct a systematic review of the literature related to the effects of functional electrical stimulation for the wrist and finger muscles of adult hemiplegic patients. METHOD: a search for studies documenting the effects of electrical stimulation on neuromuscular, musculoskeletal and functional characteristics was carried out in Medline, Lilacs and PEDro databases between February and March 2006. Data were extracted in a standardized manner from each study, and methodological quality was assessed using the PEDro scale. RESULTS: Eight randomized studies were reviewed. The scores on the methodological quality of revised studies were between 3/10 and 7/10 in the PEDro scale. Although the diversity of protocols, participants' characteristics and instrumentation prevented pooling of results, a synthesis in levels of evidence demonstrated strong evidence for positive effects of electrical stimulation on muscle strength, tonus, motor function and use of the upper limb in daily life. Moderate evidence was found for effects on dexterity and limited evidence for effects on motor coordination and independence in self-care activities. There was no evidence for gains in range of active wrist extension. CONCLUSION: Despite methodological limitations, randomized studies reported positive effects of electrical stimulation on wrist and fingers, suggesting that this therapy might be effective for promoting function of the affected upper limb of hemiplegic individuals.