title: Skeletal muscle fiber quality in older men and women.
abstract: Whole muscle strength and cross-sectional area (WMCSA), and contractile properties of chemically skinned segments from single fibers of the quadriceps were studied in 7 young men (YM, 36.5 +/- 3. 0 yr), 12 older men (OM, 74.4 +/- 5.9 yr), and 12 older women (OW, 72.1 +/- 4.3 yr). WMCSA was smaller in OM compared with YM (56.1 +/- 10.1 vs. 79.7 +/- 13.1 cm(2); P = 0.031) and in OW (44.9 +/- 7.5; P < 0.003) compared with OM. Age-related, but not sex-related, differences in strength were eliminated after adjusting for WMCSA. Maximal force was measured in 552 type I and 230 type IIA fibers. Fibers from YM (type I = 725 +/- 221; type IIA = 792 +/- 271 microN) were stronger (P < 0.001) than fibers from OM (I = 505 +/- 179; IIA = 577 +/- 262 microN) even after correcting for size. Type IIA fibers were stronger (P < 0.005) than type I fibers in YM and OM but not in OW (I = 472 +/- 154; IIA = 422 +/- 97 microN). Sex-related differences in type I and IIA fibers were dependent on fiber size. In conclusion, differences in WMCSA explain age-related differences in strength. An intrinsic defect in contractile proteins could explain weakness in single fibers from OM. Sex-related differences exist at the whole muscle and single fiber levels.
authors.affiliation: Nutrition, Exercise Physiology, and Sarcopenia Laboratory, Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston 02111, Massachusetts, USA. frontera.walter@mgh.harvard.edu
authors.forename: W R
authors.initials: WR
authors.lastname: Frontera
authors.forename: D
authors.initials: D
authors.lastname: Suh
authors.forename: L S
authors.initials: LS
authors.lastname: Krivickas
authors.forename: V A
authors.initials: VA
authors.lastname: Hughes
authors.forename: R
authors.initials: R
authors.lastname: Goldstein
authors.forename: R
authors.initials: R
authors.lastname: Roubenoff
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D012727:Sex Characteristics