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  • Title: Unchanged H-reflex during a sustained isometric submaximal plantar flexion performed with an EMG biofeedback.
    Author: Place N, Duclay J, Lepers R, Martin A.
    Journal: J Electromyogr Kinesiol; 2009 Dec; 19(6):e395-402. PubMed ID: 19216091.
    Abstract:
    The aim of this study was to assess H-reflex plasticity and activation pattern of the plantar flexors during a sustained contraction where voluntary EMG activity was controlled via an EMG biofeedback. Twelve healthy males (28.0+/-4.8 yr) performed a sustained isometric plantar flexion while instructed to maintain summed EMG root mean square (RMS) of gastrocnemius lateralis (GL) and gastrocnemius medialis (GM) muscles fixed at a target corresponding to 80% maximal voluntary contraction torque via an EMG biofeedback. Transcutaneous electrical stimulation of the posterior tibial nerve was evoked during the contraction to obtain the maximal H-reflex amplitude to maximal M-wave amplitude ratio (H(sup)/M(sup) ratio) from GL, GM and soleus (SOL) muscles. Neuromuscular function was also assessed before and immediately after exercise. Results showed a decrease in SOL activation during sustained flexion (from 65.5+/-6.4% to 42.3+/-3.8% maximal EMG, p<0.001), whereas summed EMG RMS of GL and GM remained constant (59.7+/-4.8% of maximal EMG on average). No significant change in the H(sup)/M(sup) ratio was found for SOL, GL and GM muscles. Furthermore, it appears that the decrease in maximal voluntary contraction torque (-20.4+/-2.9%, p<0.001) was related to both neural and contractile impairment. Overall, these findings indicate that the balance between excitation and inhibition affecting the motoneuron pool remains constant during a sustained contraction where myoelectrical activity is controlled via an EMG biofeedback or let free to vary.
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