title: Muscle fascicle shortening behaviour of vastus lateralis during a maximal force-velocity test.
abstract: OBJECTIVE
  Muscle fascicles-tendon interactions are the main determinant in production of high joint velocity. Currently, no study has investigated the muscle fascicles behaviour of knee extensor muscles until the highest reachable velocity (e.g., unloaded knee extension). We aimed to track the changes in vastus lateralis fascicles length during knee extensions to quantify muscle fascicles and tendinous tissues contributions to muscle-tendon unit shortening and to determine maximal muscle fascicles shortening velocity.
  
  
  METHODS
  Fifteen participants performed isokinetic and isoinertial knee extensions, and ultrafast ultrasound imaging was used to observe the vastus lateralis fascicles from low to very high joint velocity.
  
  
  RESULTS
  The muscle fascicles shortening velocity increased linearly with the increase in knee joint velocity up to the maximal joint velocity (mean R2= 0.93 ± 0.08). Muscle fascicles contribution to muscle-tendon unit shortening velocity was almost constant regardless of the condition (83 ± 23%). Using Hill's equation, the maximal velocity of knee joint and muscle fascicles was determined at 1000 ± 489°s-1and 5.1 ± 2.0 L0s-1(47.4 ± 18.7 cm s-1), respectively.
  
  
  CONCLUSIONS
  Contribution of muscle fascicles to the muscle-tendon unit shortening velocity was much higher for the vastus lateralis in this study compared to the gastrocnemius medialis in two previous studies. Moreover, this contribution of muscle fascicles shortening velocity was constant whatever the velocity condition, even at the highest reachable velocity. Thus, the vastus lateralis fascicles shortening velocity increases linearly with the knee joint velocity until high velocities and its behaviour strongly accorded with the classical Hill's force-velocity relationship.
authors.affiliation: Laboratory "Movement, Interactions, Performance" (EA 4334), Faculty of Sport Sciences, University of Nantes, 25 bis Boulevard Guy Mollet, BP 72206, 44322, Nantes Cedex 3, France.
authors.forename: Hugo
authors.initials: H
authors.lastname: Hauraix
authors.affiliation: Laboratory "Movement, Interactions, Performance" (EA 4334), Faculty of Sport Sciences, University of Nantes, 25 bis Boulevard Guy Mollet, BP 72206, 44322, Nantes Cedex 3, France. sylvain.dorel@univ-nantes.fr.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Dorel
authors.affiliation: Laboratory Sport, Expertise and Performance (EA 7370), Research Department, French Institute of Sport (INSEP), Paris, France.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Rabita
authors.affiliation: Laboratory Sport, Expertise and Performance (EA 7370), Research Department, French Institute of Sport (INSEP), Paris, France.
authors.forename: Gaël
authors.initials: G
authors.lastname: Guilhem
authors.affiliation: Laboratory "Movement, Interactions, Performance" (EA 4334), Faculty of Sport Sciences, University of Nantes, 25 bis Boulevard Guy Mollet, BP 72206, 44322, Nantes Cedex 3, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Nordez
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D004576:Electromyography / Q000379:methods; D006801:Humans; D007717:Knee / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D013710:Tendons / Q000502:physiology*; D055815:Young Adult
keywords: Fascicles–tendon interactions; Force–velocity relationship; High velocity; Knee extension; Ultrafast ultrasound