title: Inverse activation between the deeper vastus intermedius and superficial muscles in the quadriceps during dynamic knee extensions.
abstract: BACKGROUND
  We sought to determine the neuromuscular activation patterns of 4 synergistic muscles of the quadriceps femoris (QF), including the vastus intermedius (VI) muscle, during dynamic knee extensions.
  
  
  METHODS
  Nine healthy men performed dynamic knee extensions in the range of 20-100% of the one-repetition maximum (1RM) load. Surface electromyography (EMG) was recorded from the 4 muscles of the QF.
  
  
  RESULTS
  The normalized EMG amplitude of the VI was significantly higher at knee joint angles between 90° and 115° during both the concentric and eccentric phases, and it was significantly lower between 140° and 165° during concentric and eccentric phases, compared with those of vastus lateralis at 60-100% of 1RM load (P < 0.05).
  
  
  CONCLUSIONS
  These results suggest that the VI plays a key role during dynamic knee extension with flexed joint angles and specifically contributes to the initial concentric and final eccentric phases of knee joint movements.
authors.affiliation: Research Center of Health, Physical Fitness & Sports, Nagoya University, Furo, Chikusa, Nagoya, Aichi 4648601, Japan. akima@nagoya-u.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Akima
authors.forename: Akira
authors.initials: A
authors.lastname: Saito
mesh_terms: D000293:Adolescent; D000328:Adult; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007717:Knee / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology; D008297:Male; D052097:Quadriceps Muscle / Q000502:physiology*