title: Single-fiber MHC polymorphic expression is unaffected by sprint cycle training.
abstract: OBJECTIVE
  The present investigation examined single-fiber MHC alterations in response to high-intensity, short-duration, sprint cycle training.
  
  
  METHODS
  Ten untrained college-age male subjects participated in 8 wk of a progressive sprint cycle training program. Training involved 15-s maximal sprints separated by 5 min of rest beginning with four sprints x 2 d in week 1 and increasing to six sprints x 3 d at week 8. Muscle samples from the vastus lateralis were obtained before and after training. A 30-s sprint cycle test was used to evaluate performance before and after training.
  
  
  RESULTS
  For the 30-s sprint, mean power and total work increased from pre to post. Single-fiber analyses revealed a reduction in the MHC IIx isoform (2.0 +/- 1.0 to 0.2 +/- 0.1%, pre to post, P < 0.05) and an increase in MHC IIa (P = 0.08), whereas there was no change in hybrid fiber composition (total hybrids = 24%). Generally, MHC IIa content increased and MHC IIx decreased (P < 0.05) as demonstrated by homogenate analyses of tissue samples.
  
  
  CONCLUSIONS
  We report that as little as 32 min of high-intensity sprint cycle training over 8 wk is sufficient to improve sprinting performance. This training response is accompanied by an increase in MHC IIa and reduction in MHC IIx content of the vastus lateralis. However, short-duration, high-intensity, sprint cycle training does not cause a reduction in hybrid muscle fiber content.
authors: Department of Exercise Sciences, Human Performance Research Center, Brigham Young University, Provo, UT 84602, USA. allen_parcell@byu.edu
authors: Allen C
authors: AC
authors: Parcell
authors: Robert D
authors: RD
authors: Sawyer
authors: Micah J
authors: MJ
authors: Drummond
authors: Brock
authors: B
authors: O'Neil
authors: Nathan
authors: N
authors: Miller
authors: Mandy T
authors: MT
authors: Woolstenhulme
mesh_terms: D000328:Adult; D001642:Bicycling; D006801:Humans; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000235:genetics* / Q000378:metabolism; D011110:Polymorphism, Genetic; D014481:United States
chemical_list: D018995:Myosin Heavy Chains