title: Age- and gender-related differences in maximum shortening velocity of skeletal muscle fibers.
abstract: OBJECTIVE
  To determine age- and gender-related differences in maximum unloaded shortening velocity (Vo) of Type I and IIA single muscle fibers. Muscle fibers must have a broad range of contractile velocities to generate the full range of power required for varied activities.
  
  
  METHODS
  Percutaneous needle biopsies of the vastus lateralis were obtained from 31 healthy subjects (n = 7 young men [YM], n = 7 young women [YW], n = 12 older men [OM], n = 12 older women [OW]). The slack test was used to determine Vo of individual fibers; 916 muscle fibers were chemically skinned. Fiber type was determined by myosin heavy chain isoform identification.
  
  
  RESULTS
  Among men, Vo (fiber lengths/sec) was reduced with age in Type IIA fibers (OM vs. YM: 1.78 vs. 2.14; P < 0.05) but unchanged in Type I fibers. Among women, Vo was reduced with age in Type I fibers (OW vs. YW: 0.70 vs. 0.75; P < 0.05) but not IIA. OW had a lower Vo than did OM in both fiber types (Type I: OW = 0.70, OM = 0.77; Type IIA: OW = 1.51, OM = 1.78; P < 0.05). YW did not differ from YM.
  
  
  CONCLUSIONS
  Both age and gender affect Vo. Age- and gender-related differences in Vo may partially explain the impairments in muscle function that occur with aging and the greater impairment in muscle function observed in OW compared with that observed in OM.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
authors.forename: L S
authors.initials: LS
authors.lastname: Krivickas
authors.forename: D
authors.initials: D
authors.lastname: Suh
authors.forename: J
authors.initials: J
authors.lastname: Wilkins
authors.forename: V A
authors.initials: VA
authors.lastname: Hughes
authors.forename: R
authors.initials: R
authors.lastname: Roubenoff
authors.forename: W R
authors.initials: WR
authors.lastname: Frontera
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D012737:Sex Factors