title: A "functional biopsy" of muscle properties in sprinters and distance runners.
abstract: OBJECTIVE
  Fast- and slow-twitch human muscle fibers exhibit large (two- to threefold) differences in metabolic enzyme activities and contractile economy. We asked whether comparable flux differences are evident in the muscles of athletes specializing in extremely different (i.e., sprint and long-distance) running events.
  
  
  METHODS
  We took an in vivo "functional biopsy" of the ankle dorsiflexor muscles of 17 members of a university track team by using (31)P magnetic resonance spectroscopy. Ten sprinters (SPR) and seven distance runners (DIS) performed rapid isometric dorsiflexions against the resistance of a plastic foot holder. The contractile cost of exercise and glycolytic flux were calculated from changes in pH, [PCr], and [P(i)] during ischemic exercise, and oxidative capacity was calculated from PCr recovery kinetics after aerobic exercise.
  
  
  RESULTS
  Contractile costs were 47% higher in SPR than in DIS, whereas oxidative capacities were 52% higher in DIS than in SPR. Surprisingly, glycolytic ATP production was similar in the two groups.
  
  
  CONCLUSIONS
  The muscles of SPR and DIS exhibit clear differences in energetic properties, but these differences are smaller than the two- to three-fold variations seen in the properties of individual muscle fibers.
authors.affiliation: Department of Radiology, University of Washington Medical Center, Seattle, 98195-7115, USA.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Crowther
authors.forename: Sharon A
authors.initials: SA
authors.lastname: Jubrias
authors.forename: Rodney K
authors.initials: RK
authors.lastname: Gronka
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Conley
mesh_terms: D000293:Adolescent; D000328:Adult; D001707:Biopsy, Needle; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000473:pathology / Q000502:physiology*; D010806:Physical Education and Training / Q000379:methods*; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D011336:Probability; D012420:Running / Q000502:physiology; D012680:Sensitivity and Specificity; D014142:Track and Field