title: Human muscle fascicle behavior in agonist and antagonist isometric contractions.
abstract: BACKGROUND
  The aim of this study was to compare, at a given level of electromyographic (EMG) activity, the behavior of dorsiflexor and plantarflexor muscles as assessed via their architecture (pennation angle and fiber length) during agonist or antagonist isometric contractions.
  
  
  METHODS
  Real-time ultrasonography and EMG activity of gastrocnemius medialis (GM) and tibialis anterior (TA) muscles were obtained while young males performed ramp isometric contractions in dorsi- and plantarflexion.
  
  
  RESULTS
  For both muscles, at a similar level of EMG activity, fiber length was longer, and pennation angle was smaller, during antagonist than during agonist contractions.
  
  
  CONCLUSIONS
  These results indicate that, at similar levels of EMG activity, GM and TA muscles elicit a higher mechanical output while acting as an antagonist. These findings have important implications for muscle function testing. They show that estimation of antagonistic force using the common method based on the EMG/net torque relationship yields underestimated values.
authors.affiliation: Laboratoire d'Automatique, de Mécanique, et d'Informatique industrielles et Humaines, FRE CNRS 3304, Université de Valenciennes et du Hainaut-Cambrésis, F-59313 Valenciennes Cedex 09, France. emilie.simoneau@univ-valenciennes.fr
authors.forename: Emilie M
authors.initials: EM
authors.lastname: Simoneau
authors.forename: Stefano
authors.initials: S
authors.lastname: Longo
authors.forename: Olivier R
authors.initials: OR
authors.lastname: Seynnes
authors.forename: Marco V
authors.initials: MV
authors.lastname: Narici
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000294:innervation; D001696:Biomechanical Phenomena; D004576:Electromyography / Q000379:methods; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D019415:Torque; D018608:Ultrasonography, Doppler