title: Aging, muscle fiber type, and contractile function in sprint-trained athletes.
abstract: Biopsy samples were taken from the vastus lateralis of 18- to 84-yr-old male sprinters (n = 91). Fiber-type distribution, cross-sectional area, and myosin heavy chain (MHC) isoform content were identified using ATPase histochemistry and SDS-PAGE. Specific tension and maximum shortening velocity (V(o)) were determined in 144 single skinned fibers from younger (18-33 yr, n = 8) and older (53-77 yr, n = 9) runners. Force-time characteristics of the knee extensors were determined by using isometric contraction. The cross-sectional area of type I fibers was unchanged with age, whereas that of type II fibers was reduced (P < 0.001). With age there was an increased MHC I (P < 0.01) and reduced MHC IIx isoform content (P < 0.05) but no differences in MHC IIa. Specific tension of type I and IIa MHC fibers did not differ between younger and older subjects. V(o) of fibers expressing type I MHC was lower (P < 0.05) in older than in younger subjects, but there was no difference in V(o) of type IIa MHC fibers. An aging-related decline of maximal isometric force (P < 0.001) and normalized rate of force development (P < 0.05) of knee extensors was observed. Normalized rate of force development was positively associated with MHC II (P < 0.05). The sprint-trained athletes experienced the typical aging-related reduction in the size of fast fibers, a shift toward a slower MHC isoform profile, and a lower V(o) of type I MHC fibers, which played a role in the decline in explosive force production. However, the muscle characteristics were preserved at a high level in the oldest runners, underlining the favorable impact of sprint exercise on aging muscle.
authors.affiliation: Dept. of Health Sciences, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland.
authors.forename: Marko T
authors.initials: MT
authors.lastname: Korhonen
authors.forename: Alexander
authors.initials: A
authors.lastname: Cristea
authors.forename: Markku
authors.initials: M
authors.lastname: Alén
authors.forename: Keijo
authors.initials: K
authors.lastname: Häkkinen
authors.forename: Sarianna
authors.initials: S
authors.lastname: Sipilä
authors.forename: Antti
authors.initials: A
authors.lastname: Mero
authors.forename: Jukka T
authors.initials: JT
authors.lastname: Viitasalo
authors.forename: Lars
authors.initials: L
authors.lastname: Larsson
authors.forename: Harri
authors.initials: H
authors.lastname: Suominen
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology* / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000502:physiology*; D012420:Running / Q000502:physiology*