title: Does the mechanical work in running change during the VO2 slow component?
abstract: OBJECTIVE
  The origin of the slow component is not fully understood. The mechanical hypothesis is one of the potential factors, because an increase in external mechanical work with fatigue was previously reported for a constant velocity run. The purpose of this study was to determine whether a change in mechanical work could occur during the development of the VO2 slow component under the effect of fatigue.
  
  
  METHODS
  Twelve regional-level competitive runners performed a square-wave transition, corresponding to 95% of the speed associated with peak VO2 obtained during an incremental test. The VO2 response was fit with a classical model including two exponential functions. A specific treadmill with three-dimensional force transducers was used to measure the ground reaction force. Kinetic work (W(kin)), potential work (W(pot)), external work (W(ext)), and an index of internal work (W(int)) per unit of distance were quantified continuously.
  
  
  RESULTS
  During the slow component of VO2, a significant increase in W (P< 0.01), no change in W, and a significant decrease in W and W index (P< 0.05, P< 0.001, respectively) were observed.
  
  
  CONCLUSIONS
  The present study showed that the slow component of VO2 did not result partly from a change in mechanical work under the effect of fatigue. Nevertheless, the decrease in stride frequency (P< 0.001) and contact time (P< 0.001) suggested an alternative mechanical explanation. The slow component during running may be due to the cost of generating force or to alterations in the storage and recoil of elastic energy, and not to the external mechanical work.
authors.affiliation: Laboratoire Sport Performance et Santé, Faculté des Sciences du Sport, Université de Montpellier I, Montpellier, France. f.borrani@staps.univ-montp1.fr
authors.forename: Fabio
authors.initials: F
authors.lastname: Borrani
authors.forename: Robin
authors.initials: R
authors.lastname: Candau
authors.forename: Stephane
authors.initials: S
authors.lastname: Perrey
authors.forename: Guillaume Y
authors.initials: GY
authors.lastname: Millet
authors.forename: Gregoire P
authors.initials: GP
authors.lastname: Millet
authors.forename: Jean-Denis
authors.initials: JD
authors.lastname: Rouillon
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005080:Exercise Test; D006801:Humans; D007700:Kinetics; D018763:Muscle Fatigue / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D012420:Running / Q000502:physiology*