title: Dynamics of corticospinal changes during and after high-intensity quadriceps exercise.
abstract: This study tested the hypothesis that during fatiguing quadriceps exercise, supraspinal fatigue develops late, is associated with both increased corticospinal excitability and inhibition and recovers quickly. Eight subjects performed 20 s contractions [15 s at 50% maximal voluntary contraction (MVC) followed by 5 s MVC] separated by a 10 s rest period until task failure. Transcranial magnetic stimulation (TMS) and electrical femoral nerve stimulation (PNS) were delivered ∼ 2 s apart during 50% MVC, during MVC and after MVC in relaxed muscle. Voluntary activation was assessed by TMS (VATMS) immediately before and after exercise and then three times over a 6 min recovery period. During exercise, MVC and twitch force evoked by PNS in relaxed muscle decreased progressively to 48 ± 8 and 36 ± 16% of control values, respectively (both P < 0.01). Significant changes in voluntary activation assessed by PNS and twitch evoked by TMS during MVC were observed during the last quarter of exercise only (from 96.4 ± 1.7 to 86 ± 13%, P = 0.03 and from 0.76 ± 0.8 to 4.9 ± 4.7% MVC, P = 0.02, from baseline to task failure, respectively). The TMS-induced silent period increased linearly during both MVC (by ∼ 79 ms) and 50% MVC (by ∼ 63 ms; both P < 0.01). Motor-evoked potential amplitude did not change during the protocol at any force levels. Both silent period and VATMS recovered within 2 min postexercise, whereas MVC and twitch force evoked by PNS in relaxed muscle recovered to only 84 ± 9 and 73 ± 17% of control values 6 min after exercise, respectively. In conclusion, high-intensity single-joint quadriceps exercise induces supraspinal fatigue near task failure, with increased intracortical inhibition and, in contrast to previous upper-limb results, unchanged corticospinal excitability. These changes recover rapidly after task failure, emphasizing the need to measure corticospinal adaptations immediately at task failure to avoid underestimation of exercise-induced corticospinal changes.
authors.affiliation: Université Grenoble-Alpes, Laboratoire HP2, F-38000, Grenoble, France INSERM, U1042, F-38000, Grenoble, France Laboratoire Motricité Humaine, Education, Sport, Santé, Université de Toulon, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Gruet
authors.affiliation: Université de Lyon, F-42023, Saint-Etienne, France Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: John
authors.initials: J
authors.lastname: Temesi
authors.affiliation: Université Grenoble-Alpes, Laboratoire HP2, F-38000, Grenoble, France INSERM, U1042, F-38000, Grenoble, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rupp
authors.affiliation: Université Grenoble-Alpes, Laboratoire HP2, F-38000, Grenoble, France INSERM, U1042, F-38000, Grenoble, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Levy
authors.affiliation: Université Grenoble-Alpes, Laboratoire HP2, F-38000, Grenoble, France INSERM, U1042, F-38000, Grenoble, France sverges@chu-grenoble.fr.
authors.forename: Samuel
authors.initials: S
authors.lastname: Verges
authors.affiliation: INSERM, U1042, F-38000, Grenoble, France Université de Lyon, F-42023, Saint-Etienne, France Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Guillaume Y
authors.initials: GY
authors.lastname: Millet
mesh_terms: D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007717:Knee / Q000502:physiology; D007719:Knee Joint / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods