title: Slower but not faster unilateral fatiguing knee extensions alter contralateral limb performance without impairment of maximal torque output.
abstract: OBJECTIVE
  The purpose of the present study was to examine the effects of unilateral fatigue of the knee extensors at different movement velocities on neuromuscular performance in the fatigued and non-fatigued leg.
  
  
  METHODS
  Unilateral fatigue of the knee extensors was induced in 11 healthy young men (23.7 ± 3.8 years) at slower (60°/s; FAT60) and faster movement velocities (240°/s; FAT240) using an isokinetic dynamometer. A resting control (CON) condition was included. The fatigue protocols consisted of five sets of 15 maximal concentric knee extensions using the dominant leg. Before and after fatigue, peak isokinetic torque (PIT) and time to PIT (TTP) of the knee extensors as well as electromyographic (EMG) activity of vastus medialis, vastus lateralis, and biceps femoris muscles were assessed at 60 and 240°/s movement velocities in the fatigued and non-fatigued leg.
  
  
  RESULTS
  In the fatigued leg, significantly greater PIT decrements were observed following FAT60 and FAT240 (11-19%) compared to CON (3-4%, p = .002, d = 2.3). Further, EMG activity increased in vastus lateralis and biceps femoris muscle following FAT240 only (8-28%, 0.018 ≤ p ≤ .024, d = 1.8). In the non-fatigued leg, shorter TTP values were found after the FAT60 protocol (11-15%, p = .023, d = 2.4). No significant changes were found for EMG data in the non-fatigued leg.
  
  
  CONCLUSIONS
  The present study revealed that both slower and faster velocity fatiguing contractions failed to show any evidence of cross-over fatigue on PIT. However, unilateral knee extensor fatigue protocols conducted at slower movement velocities (i.e., 60°/s) appear to modulate torque production on the non-fatigued side (evident in shorter TTP values).
authors.affiliation: Division of Training and Movement Science, Research Focus Cognition Sciences, University of Potsdam, Am Neuen Palais 10, Building 12, 14469, Potsdam, Germany. prieske@uni-potsdam.de.
authors.forename: Olaf
authors.identifier: http://orcid.org/0000-0003-4475-4413
authors.initials: O
authors.lastname: Prieske
authors.affiliation: Faculty of Kinesiology, University of Calgary, Calgary, Canada.
authors.forename: Saied J
authors.initials: SJ
authors.lastname: Aboodarda
authors.affiliation: Division of Training and Movement Science, Research Focus Cognition Sciences, University of Potsdam, Am Neuen Palais 10, Building 12, 14469, Potsdam, Germany.
authors.forename: José A
authors.initials: JA
authors.lastname: Benitez Sierra
authors.affiliation: School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, NF, Canada.
authors.forename: David G
authors.initials: DG
authors.lastname: Behm
authors.affiliation: Division of Training and Movement Science, Research Focus Cognition Sciences, University of Potsdam, Am Neuen Palais 10, Building 12, 14469, Potsdam, Germany.
authors.forename: Urs
authors.initials: U
authors.lastname: Granacher
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods; D006801:Humans; D007717:Knee / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D052097:Quadriceps Muscle / Q000502:physiology; D019415:Torque; D055815:Young Adult
keywords: Central activation; Cross-over fatigue; Electromyography; Isokinetic; Motor function; Movement velocity