title: Aging of skeletal muscle: a 12-yr longitudinal study.
abstract: The present study examines age-related changes in skeletal muscle size and function after 12 yr. Twelve healthy sedentary men were studied in 1985-86 (T1) and nine (initial mean age 65.4 +/- 4.2 yr) were reevaluated in 1997-98 (T2). Isokinetic muscle strength of the knee and elbow extensors and flexors showed losses (P < 0.05) ranging from 20 to 30% at slow and fast angular velocities. Computerized tomography (n = 7) showed reductions (P < 0.05) in the cross-sectional area (CSA) of the thigh (12.5%), all thigh muscles (14.7%), quadriceps femoris muscle (16.1%), and flexor muscles (14. 9%). Analysis of covariance showed that strength at T1 and changes in CSA were independent predictors of strength at T2. Muscle biopsies taken from vastus lateralis muscles (n = 6) showed a reduction in percentage of type I fibers (T1 = 60% vs. T2 = 42%) with no change in mean area in either fiber type. The capillary-to-fiber ratio was significantly lower at T2 (1.39 vs. 1. 08; P = 0.043). Our observations suggest that a quantitative loss in muscle CSA is a major contributor to the decrease in muscle strength seen with advancing age and, together with muscle strength at T1, accounts for 90% of the variability in strength at T2.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Harvard Medical School and Spaulding Rehabilitation Hospital, Boston, MA 02114, USA. frontera.walter@mgh.harvard.edu
authors.forename: W R
authors.initials: WR
authors.lastname: Frontera
authors.forename: V A
authors.initials: VA
authors.lastname: Hughes
authors.forename: R A
authors.initials: RA
authors.lastname: Fielding
authors.forename: M A
authors.initials: MA
authors.lastname: Fiatarone
authors.forename: W J
authors.initials: WJ
authors.lastname: Evans
authors.forename: R
authors.initials: R
authors.lastname: Roubenoff
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D002196:Capillaries / Q000254:growth & development / Q000502:physiology; D004551:Elbow Joint / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction; D007719:Knee Joint / Q000502:physiology; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D024510:Muscle Development; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply / Q000254:growth & development / Q000502:physiology*; D013997:Time Factors; D014057:Tomography, X-Ray Computed