Surprisingly little attention has been devoted to the role played by the intrinsic muscles of the human foot. The aim of this study was to quantify the capabilities of the flexor digitorum brevis (FDB) muscle to contribute to upright postural control. The approaches consisted of analysis of the effects of FDB contraction elicited by external electrical stimulation and quantification of the magnitude of FDB torque generation. The results showed the FDB can produce significant changes in static posture by itself as shown by changes in the center of pressure. Moreover, the FDB contribution to counterbalance the gravity's toppling force was estimated at around 14.5% of the total required active torque at the ankle to keep the subject from falling. A posteriori functional analysis during horizontal perturbations showed high and self-sustained activity of FDB. These results demonstrated that the FDB has a significant capability of contributing to postural control.
© Revista Brasileira de FisioterapiaChanges in FDB and soleus muscle activity after a train of stimuli during upright stance Alterações pós-trem de estímulo, na atividade dos músculos FDB e sóleus durante a postura ortostática Liria A. Okai 1,2 , André F. Kohn 1 AbstractBackground: Evidence of self-sustained muscle activation following a brief electrical stimulation has been reported in the literature for certain muscles. Objectives: This report shows that the foot muscle (Flexor Digitorum Brevis -FDB) shows a self-sustained increase in muscle activity during upright stance in some subjects following a train of stimuli to the tibial nerve. Methods: Healthy subjects were requested to stand upright and surface EMG electrodes were placed on the FDB, Soleus and Tibialis Anterior muscles. After background muscle activity (BGA) acquisition, a 50 Hz train of stimuli was applied to the tibial nerve at the popliteal fossa. The root mean square values (RMS) of the BGA and the post-stimulus muscle activation were computed. Results: There was a 13.8% average increase in the FDB muscle EMG amplitude with respect to BGA after the stimulation was turned off. The corresponding post-stimulus Soleus EMG activity decreased by an average of 9.2%. We hypothesize that the sustained contraction observed in the FDB following stimulus may be evidence of persistent inward currents (PIC) generated in FDB spinal motoneurons. The post-stimulus decrease in soleus activity may have occurred due to the action of inhibitory interneurons caused by the PICs, which were triggered by the stimulus train. Conclusions: These sustained post-stimulation changes in postural muscle activity, found in different levels in different subjects, may be part of a set of possible responses that contribute to overall postural control.Keywords: physical therapy; posture; foot; human; electromyography; motor activity. ResumoContextualização: Existem evidências de ativação autossustentada em certos músculos pós-estimulação elétrica. Objetivos: Mostrar que, em alguns sujeitos, o músculo do pé (Flexor Digitorum Brevis -FDB) também pode apresentar aumento de atividade autossustentada na posição ortostática pós-trem de estímulo no nervo tibial. Métodos: Sujeitos foram solicitados a permanecer na posição ortostática e sinais eletromiográficos foram coletados dos músculos FDB, sóleus e tibial anterior do membro inferior direito. Após a aquisição dos sinais eletromiográficos base (sem estimulação -BGA), um trem de estímulos de 50 Hz foi aplicado no nervo tibial (fossa poplítea).Foram analisados os valores RMS dos dados BGA e dos sinais coletados pós-estímulo. Resultados: Ao fim do estímulo, houve um aumento de 13,8% da atividade muscular do FDB em comparação com BGA. O mesmo fenômeno não aconteceu com o músculo sóleus, que apresentou uma diminuição de 9,2% da sua atividade pós-estímulo. Uma das hipóteses para a geração pós-estímulo da contração sustentada do FDB seria a da geração de corrente de entrada persistente (PIC) nos motoneurônios espinais do FDB. A diminuição da at...
OKAI, L.A. Influência do músculo Flexor Digitorum Brevis (FDB) no controle da postura ortostática. 2005. 79 f.
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