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  • Title: The nature of facilitation of leg muscle motor evoked potentials by knee flexion.
    Author: Izumi SI, Furukawa T, Koyama Y, Ishida A.
    Journal: Somatosens Mot Res; 2001; 18(4):322-9. PubMed ID: 11794734.
    Abstract:
    Knee flexion is a movement that initiates rising from a sitting position, which is a common therapeutic exercise for patients unable to ambulate. We investigated how voluntary isometric biceps femoris contraction affects motor evoked potential (MEP) amplitude following transcranial magnetic stimulation, background electromyographic (EMG) amplitude, and H-reflex amplitude in ipsilateral leg muscles. Subjects were seated on the edge of a bed with their hips and knees flexed at 90 degrees, and the soles of their feet on the floor. MEP and background EMG were recorded from the tibialis anterior (TA) and soleus (SOL), and H reflexes from SOL of 30 volunteers. Background EMG and MEP also were recorded while voluntarily contracting tested muscles. Biceps femoris contraction increased MEP and background EMG for TA and SOL (p < 0.01). Maximal background EMG and MEP increased with increasing voluntary contraction of tested muscles (p < 0.005). Regression slope differed little between TA and SOL. Biceps femoris contraction facilitated MEP comparably for TA and SOL, while SOL background EMG exceeded that of TA (p < 0.02). The relationship between MEP facilitation and background EMG changed to favor more efficient facilitation in TA (p < 0.05), but not SOL (p > 0.1). MEP recorded from TA and SOL with subthreshold stimuli using needle electrodes were more frequent with biceps femoris contraction (p < 0.04). H-reflex amplitude of SOL decreased during biceps femoris contraction (p < 0.001). We concluded that biceps femoris contraction affects leg muscle MEP, background EMG, and H reflexes differently.
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