title: Changes in voluntary activation assessed by transcranial magnetic stimulation during prolonged cycling exercise.
abstract: Maximal central motor drive is known to decrease during prolonged exercise although it remains to be determined whether a supraspinal deficit exists, and if so, when it appears. The purpose of this study was to evaluate corticospinal excitability and muscle voluntary activation before, during and after a 4-h cycling exercise. Ten healthy subjects performed three 80-min bouts on an ergocycle at 45% of their maximal aerobic power. Before exercise and immediately after each bout, neuromuscular function was evaluated in the quadriceps femoris muscles under isometric conditions. Transcranial magnetic stimulation was used to assess voluntary activation at the cortical level (VATMS), corticospinal excitability via motor-evoked potential (MEP) and intracortical inhibition by cortical silent period (CSP). Electrical stimulation of the femoral nerve was used to measure voluntary activation at the peripheral level (VAFNES) and muscle contractile properties. Maximal voluntary force was significantly reduced after the first bout (13 ± 9%, P<0.01) and was further decreased (25 ± 11%, P<0.001) at the end of exercise. CSP remained unchanged throughout the protocol. Rectus femoris and vastus lateralis but not vastus medialis MEP normalized to maximal M-wave amplitude significantly increased during cycling. Finally, significant decreases in both VATMS and VAFNES (∼ 8%, P<0.05 and ∼ 14%, P<0.001 post-exercise, respectively) were observed. In conclusion, reductions in VAFNES after a prolonged cycling exercise are partly explained by a deficit at the cortical level accompanied by increased corticospinal excitability and unchanged intracortical inhibition. When comparing the present results with the literature, this study highlights that changes at the cortical and/or motoneuronal levels depend not only on the type of exercise (single-joint vs. whole-body) but also on exercise intensity and/or duration.
authors.affiliation: INSERM U1042, Grenoble, France ; Université de Lyon, Saint-Etienne, France ; MIP, Nantes, France.
authors.forename: Marc
authors.initials: M
authors.lastname: Jubeau
authors.affiliation: INSERM U1042, Grenoble, France ; Laboratoire HP2, Grenoble Alpes University, Grenoble, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rupp
authors.affiliation: Movement To Health (M2H), Montpellier-I University, Euromov, France.
authors.forename: Stephane
authors.initials: S
authors.lastname: Perrey
authors.affiliation: Université de Lyon, Saint-Etienne, France.
authors.forename: John
authors.initials: J
authors.lastname: Temesi
authors.affiliation: INSERM U1042, Grenoble, France ; Laboratoire HP2, Grenoble Alpes University, Grenoble, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Wuyam
authors.affiliation: INSERM U1042, Grenoble, France ; Laboratoire HP2, Grenoble Alpes University, Grenoble, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Levy
authors.affiliation: INSERM U1042, Grenoble, France ; Laboratoire HP2, Grenoble Alpes University, Grenoble, France.
authors.forename: Samuel
authors.initials: S
authors.lastname: Verges
authors.affiliation: INSERM U1042, Grenoble, France ; Université de Lyon, Saint-Etienne, France ; Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada.
authors.forename: Guillaume Y
authors.initials: GY
authors.lastname: Millet
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005267:Femoral Nerve / Q000502:physiology; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology; D052097:Quadriceps Muscle / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation