title: Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults.
abstract: Resistance training (RT) has shown the most promise in reducing/reversing effects of sarcopenia, although the optimum regime specific for older adults remains unclear. We hypothesized myofiber hypertrophy resulting from frequent (3 days/wk, 16 wk) RT would be impaired in older (O; 60-75 yr; 12 women, 13 men), sarcopenic adults compared with young (Y; 20-35 yr; 11 women, 13 men) due to slowed repair/regeneration processes. Myofiber-type distribution and cross-sectional area (CSA) were determined at 0 and 16 wk. Transcript and protein levels of myogenic regulatory factors (MRFs) were assessed as markers of regeneration at 0 and 24 h postexercise, and after 16 wk. Only Y increased type I CSA 18% (P < 0.001). O showed smaller type IIa (-16%) and type IIx (-24%) myofibers before training (P < 0.05), with differences most notable in women. Both age groups increased type IIa (O, 16%; Y, 25%) and mean type II (O, 23%; Y, 32%) size (P < 0.05). Growth was generally most favorable in young men. Percent change scores on fiber size revealed an age x gender interaction for type I fibers (P < 0.05) as growth among Y (25%) exceeded that of O (4%) men. Myogenin and myogenic differentiation factor D (MyoD) mRNAs increased (P < 0.05) in Y and O, whereas myogenic factor (myf)-5 mRNA increased in Y only (P < 0.05). Myf-6 protein increased (P < 0.05) in both Y and O. The results generally support our hypothesis as 3 days/wk training led to more robust hypertrophy in Y vs. O, particularly among men. However, this differential hypertrophy adaptation was not explained by age variation in MRF expression.
authors.affiliation: UAB Dept. of Physiology and Biophysics, Muscle Research Laboratory, GRECC/11G VA Medical Center, 1530 3rd Ave., South Birmingham, AL 35294-0001, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Kosek
authors.forename: Jeong-Su
authors.initials: JS
authors.lastname: Kim
authors.forename: John K
authors.initials: JK
authors.lastname: Petrella
authors.forename: James M
authors.initials: JM
authors.lastname: Cross
authors.forename: Marcas M
authors.initials: MM
authors.lastname: Bamman
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D006984:Hypertrophy / Q000473:pathology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D024510:Muscle Development / Q000502:physiology*; D017570:MyoD Protein / Q000235:genetics / Q000502:physiology; D009210:Myofibrils / Q000473:pathology* / Q000502:physiology*; D051787:Myogenic Regulatory Factor 5 / Q000235:genetics / Q000502:physiology; D018006:Myogenic Regulatory Factors / Q000235:genetics / Q000502:physiology; D018008:Myogenin / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D012727:Sex Characteristics; D013997:Time Factors; D014891:Weight Lifting
chemical_list: C497417:MYF5 protein, human; D017570:MyoD Protein; D051787:Myogenic Regulatory Factor 5; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D012333:RNA, Messenger; C063403:myogenic factor 6