title: Gender differences in resistance-training-induced myofiber hypertrophy among older adults.
abstract: We tested the hypothesis that older men (n = 9, 69 +/- 2 years) would experience greater resistance-training-induced myofiber hypertrophy than older women (n = 5, 66 +/- 1 years) following knee extensor training 3 days per week at 65-80% of one-repetition maximum for 26 weeks. Vastus lateralis biopsies were analyzed for myofiber areas, myosin heavy chain isoform distribution, and levels of mRNA for insulin-like growth factor 1 (IGF-1), IGFR1, and myogenin. Gender x Training interactions (p <.05) indicate greater myofiber hypertrophy for all three primary fiber types (I, IIa, IIx) and enhanced one-repetition maximum strength gain in men compared with women (p <.05). Covarying for serum IGF-1, dehydroepiandrosterone sulfate, or each muscle mRNA did not negate these interactions. In both genders, type IIx myofiber area distribution and myosin heavy chain type IIx distribution decreased with a concomitant increase in type IIa myofiber area distribution (p <.05). In summary, gender differences in load-induced myofiber hypertrophy among older adults cannot be explained by levels of circulating IGF-1 or dehydroepiandrosterone sulfate, or by expression of the myogenic transcripts examined.
authors.affiliation: Geriatric Research, Education, and Clinical Center, VA Medical Center, Birmingham, Alabama, USA. mbamman@uab.edu
authors.forename: Marcas M
authors.initials: MM
authors.lastname: Bamman
authors.forename: Vernishia J
authors.initials: VJ
authors.lastname: Hill
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Adams
authors.forename: Fadia
authors.initials: F
authors.lastname: Haddad
authors.forename: Carla J
authors.initials: CJ
authors.lastname: Wetzstein
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Gower
authors.forename: Ali
authors.initials: A
authors.lastname: Ahmed
authors.forename: Gary R
authors.initials: GR
authors.lastname: Hunter
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D015331:Cohort Studies; D015444:Exercise; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology; D018008:Myogenin / Q000032:analysis / Q000378:metabolism*; D010806:Physical Education and Training; D012016:Reference Values; D012680:Sensitivity and Specificity; D012737:Sex Factors
chemical_list: C503799:MYOG protein, human; D018008:Myogenin; D007334:Insulin-Like Growth Factor I