title: Blood lactate and sEMG at different knee angles during fatiguing leg press exercise.
abstract: The purpose of this study was to examine the changes in peak power output, blood lactate concentrations and surface electromyographic activity (sEMG) of the agonist [vastus lateralis (VL) and vastus medialis (VM)] and the antagonist [biceps femoris (BF)] muscles at two angular positions intervals (90-67° and 23-0° of knee flexion), during a set of 10 repetitions leading to failure of bilateral leg press exercise. Fatiguing exercise resulted in increased blood lactate concentrations, the agonist mean rectified voltage (MRV) at 90-67° of flexion, the antagonist average MRV at 23-0° of flexion and the spectral parameter proposed by Dimitrov (FI(nsm5)) (P < 0.01-0.05). Significant decreases (P < 0.01-0.05) were observed in power output, median frequency (F(med)) of the agonist muscles at both angular position intervals and of the antagonist muscle at 90-67° of flexion. No changes were observed in the antagonist/agonist MRV activation ratio. The present data suggest that the shift of frequency spectrum to lower frequencies and the accumulation of lactate and/or H(+), but not the antagonist/agonist MRV activation ratio, may be relevant independent factors associated with fatigue.
authors.affiliation: Studies, Research and Sport Medicine Centre, Government of Navarre, Calle Sangüesa 34, 31005 Pamplona, Navarra, Spain. egorosta@cfnavarra.es
authors.forename: Esteban M
authors.initials: EM
authors.lastname: Gorostiaga
authors.forename: Ion
authors.initials: I
authors.lastname: Navarro-Amézqueta
authors.forename: Miriam
authors.initials: M
authors.lastname: González-Izal
authors.forename: Armando
authors.initials: A
authors.lastname: Malanda
authors.forename: Cristina
authors.initials: C
authors.lastname: Granados
authors.forename: Javier
authors.initials: J
authors.lastname: Ibáñez
authors.forename: Igor
authors.initials: I
authors.lastname: Setuain
authors.forename: Mikel
authors.initials: M
authors.lastname: Izquierdo
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood; D004576:Electromyography; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007719:Knee Joint / Q000502:physiology*; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D053580:Muscle Strength; D052097:Quadriceps Muscle / Q000502:physiology*; D016059:Range of Motion, Articular; D055070:Resistance Training; D013030:Spain; D015854:Up-Regulation
chemical_list: D015415:Biomarkers; D019344:Lactic Acid