title: Changes in spring-mass behavior and muscle activity during an exhaustive run at V̇O2max.
abstract: OBJECTIVE
  The aim of this study was to evaluate concomitantly the changes in leg-spring behavior and the associated modifications in the lower limb muscular activity during a constant pace run to exhaustion at severe intensity.
  
  
  METHODS
  Twelve trained runners performed a running test at the velocity associated with VO(2max) (5.1 ± 0.3 ms(-1); mean time to exhaustion: 353 ± 69s). Running step spatiotemporal parameters and spring-mass stiffness were calculated from vertical and horizontal components of ground reaction force measured by a 6.60 m long force platform system. The myoelectrical activity was measured by wireless surface electrodes on eight lower limb muscles.
  
  
  RESULTS
  The leg stiffness decreased significantly (-8.9%; P<0.05) while the vertical stiffness did not change along the exhaustive exercise. Peak vertical force (-3.5%; P<0.001) and aerial time (-9.7%; P<0.001) decreased and contact time significantly increased (+4.6%; P<0.05). The myoelectrical activity decreased significantly for triceps surae but neither vastus medialis nor vastus lateralis presented significant change. Both rectus and biceps femoris increased in the early phase of swing (+14.7%; P<0.05) and during the pre-activation phase (+16.2%; P<0.05).
  
  
  CONCLUSIONS
  The decrease in leg spring-stiffness associated with the decrease in peak vertical ground reaction force was consistent with the decline in plantarflexor activity. The biarticular rectus femoris and biceps femoris seem to play a major role in the mechanical and spatiotemporal adjustments of stride pattern with the occurrence of fatigue during such exhaustive run.
authors.affiliation: Research Department, National Institute of Sport, Expertise and Performance, INSEP, Paris, France. giuseppe.rabita@insep.fr
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Rabita
authors.forename: Antoine
authors.initials: A
authors.lastname: Couturier
authors.forename: Sylvain
authors.initials: S
authors.lastname: Dorel
authors.forename: Christophe
authors.initials: C
authors.lastname: Hausswirth
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Meur
mesh_terms: D000328:Adult; D006801:Humans; D035002:Lower Extremity / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D012420:Running / Q000502:physiology*
keywords: Fatigue; Force platform; Lower limb muscles; Spring-mass model