title: Changes in neuromuscular function after tasks involving control of EMG versus torque feedback of the same duration.
abstract: This study was designed to compare alterations in neuromuscular function after two tasks of similar duration involving the control of (1) torque level fixed at 40% maximal voluntary contraction (MVC) torque (torque task) and (2) EMG level when exerting 40% MVC torque on the knee extensor muscles. Ten healthy subjects volunteered to participate in two testing sessions separated by approximately 2 h. Contraction duration for the EMG task was fixed for each subject to the time to task failure of the torque task (104+/-20s). MVC, maximal voluntary activation level, muscle compound action potential (M-wave), peak twitch and potentiated peak doublet were assessed before and immediately after each task using electrical stimulation of the femoral nerve. Average EMG activity of quadriceps muscle increased (p<0.01) during the torque task from 27.7+/-5.4% to 46.2+/-19.3% maximal EMG, whereas torque decreased during the EMG task from 41.5+/-2.9% to 28.9+/-3.8% MVC torque. Alterations in MVC torque (p<0.01) and maximal voluntary activation level (p<0.05) were comparable at termination of the two tasks. Rate of perceived exertion was greater (p<0.05) at the end of the torque task compared to the EMG task. Despite the absence of change in the M-wave for either task, potentiated peak doublet was altered after the torque task (-18+/-14%, p<0.01), whereas there was no change after the EMG task (p>0.05). The absence of peripheral failure at the end of the EMG task could be attributed to (1) a lower intramuscular pressure allowing a lesser accumulation of metabolites and (2) a slower rate of PCr hydrolysis compared to the torque task.
authors.affiliation: INSERM ERM 207, Motricité-Plasticité Laboratory, Faculty of Sport Sciences, University of Burgundy, BP 27877, 21078 Dijon Cedex, France. nicolas.place@u-bourgogne.fr
authors.forename: Nicolas
authors.initials: N
authors.lastname: Place
authors.forename: Alain
authors.initials: A
authors.lastname: Martin
authors.forename: Romuald
authors.initials: R
authors.lastname: Lepers
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography; D005246:Feedback / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology / Q000528:radiation effects; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009424:Nervous System Physiological Phenomena; D013997:Time Factors; D019415:Torque