title: Muscle contractile function and neural control after repetitive endurance cycling.
abstract: OBJECTIVE
  To examine alterations in muscle contractile properties, cortical excitability, and voluntary activation as a consequence of 20 d of repetitive endurance cycling within a 22-d period.
  
  
  METHODS
  Eight well-trained male cyclists completed 20 prolonged cycling stages interspersed by two rest days (days 9 and 17), which replicated the 2007 Tour de France route and schedule. Isometric knee extensor torque and EMG responses of the vastus lateralis in response to percutaneous electrical stimulation and transcranial magnetic stimulation were measured before, on days 9 and 17, and 2 d after completion of Tour de France. Postexercise measurements on days 9 and 17 were taken >18 h after cessation of the previous exercise bout.
  
  
  RESULTS
  Maximal voluntary contraction of the knee extensors decreased by 20 +/- 10% (P < 0.01) during Tour de France but recovered after 2 d of rest. Peripherally evoked M-wave and potentiated twitch responses were also significantly decreased during Tour de France, up to 31 +/- 21% and 22 +/- 18%, respectively (P < 0.05), but returned to baseline values after 2 d of recovery. Voluntary activation was reduced to 75 +/- 8% (P < 0.05) during Tour de France and remained significantly depressed (79 +/- 7%, P < 0.05) after completion. The amplitude of motor evoked potentials was decreased by 44 +/- 28% (P < 0.01) on day 9 and remained significantly depressed during the remainder of, and after, Tour de France.
  
  
  CONCLUSIONS
  A reduction in knee extensor strength, which occurs after repetitive prolonged cycling exercise, is a result of both central and peripheral processes. Reduced sarcolemmal excitability and impairment of contractile mechanisms exists even after 18 h of recovery. An enduring reduction in corticomotor output persists even after 2 d of rest.
authors.affiliation: Chelsea School Research Centre, University of Brighton, Eastbourne, United Kingdom. emma.ross@brunel.ac.uk
authors.forename: Emma Z
authors.initials: EZ
authors.lastname: Ross
authors.forename: Warren
authors.initials: W
authors.lastname: Gregson
authors.forename: Karen
authors.initials: K
authors.lastname: Williams
authors.forename: Colin
authors.initials: C
authors.lastname: Robertson
authors.forename: Keith
authors.initials: K
authors.lastname: George
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001642:Bicycling / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000294:innervation / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D019415:Torque; D050781:Transcranial Magnetic Stimulation