title: Unchanged H-reflex during a sustained isometric submaximal plantar flexion performed with an EMG biofeedback.
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.
authors.affiliation: Laboratoire INSERM U887 Motricité-Plasticité, Faculté des Sciences du Sport, Université de Bourgogne, Dijon, France. nicolas.place@unige.ch
authors.forename: Nicolas
authors.initials: N
authors.lastname: Place
authors.forename: Julien
authors.initials: J
authors.lastname: Duclay
authors.forename: Romuald
authors.initials: R
authors.lastname: Lepers
authors.forename: Alain
authors.initials: A
authors.lastname: Martin
mesh_terms: D000328:Adult; D001676:Biofeedback, Psychology / Q000379:methods*; D004576:Electromyography / Q000379:methods*; D005528:Foot / Q000502:physiology; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*