title: GH administration changes myosin heavy chain isoforms in skeletal muscle but does not augment muscle strength or hypertrophy, either alone or combined with resistance exercise training in healthy elderly men.
abstract: GH administration, either alone or combined with resistance exercise training (RT), has attracted interest as a means of increasing muscle mass and strength in the elderly. In the present study, 31 healthy, elderly men [age, 74 +/- 1 yr (mean +/- SEM)] were assigned to either RT [3 sessions/wk, 3-5 sets of 8-12 repetition maximum (RM)/session] + placebo (n = 8), RT + GH (n = 8), GH (n = 8), or placebo (n = 7) in a randomized, placebo-controlled, double-blinded (RT + placebo and RT + GH) or single-blinded (GH or placebo) design. Measurements of: 1) isokinetic quadriceps muscle strength; 2) quadriceps muscle power; 3) quadriceps muscle fiber type, size, and myosin heavy chain (MHC) composition; 4) quadriceps cross-sectional area (CSA) [nuclear magnetic resonance imaging (NMRI)]; 5) body composition (dual-energy x-ray absorptiometry scanning); and 6) GH-related serum markers were performed at baseline and after 12 wk. The final GH dose was 1.77 +/- 0.18 IU x d(-1) (approximately 7.2 +/- 0.8 microg x kg(-1) x d(-1)). GH alone had no effect on isokinetic quadriceps muscle strength, power, CSA, or fiber size. However, a substantial increase in MHC 2X isoform was observed with GH administration alone, and this may be regarded as a change into a more youthful MHC composition, possibly induced by the rejuvenating of systemic IGF-I levels. RT + placebo caused substantial increases in quadriceps isokinetic strength, power, and CSA; but these RT induced improvements were not further augmented by additional GH administration. In the RT + GH group, there was a significant decrease in MHC 1 and 2X isoforms, whereas MHC 2A increased. RT, therefore, seems to overrule the changes in MHC composition induced by GH administration alone. Changes in body composition confirmed previous reports of decreased fat mass, increased fat-free mass, and unchanged bone mineral content with GH administration. A high incidence of side effects was reported. Our results do not support a role for GH as a means of increasing muscle strength or mass, either alone or combined with RT, in healthy elderly men; although GH administration alone may induce changes in MHC composition.
authors.affiliation: Sports Medicine Research Unit, Bispebjerg Hospital, DK-2400 Copenhagen NV, Denmark. klange@dadlnet.dk
authors.forename: Kai Henrik Wiborg
authors.initials: KH
authors.lastname: Lange
authors.forename: Jesper Løvind
authors.initials: JL
authors.lastname: Andersen
authors.forename: Nina
authors.initials: N
authors.lastname: Beyer
authors.forename: Fredrik
authors.initials: F
authors.lastname: Isaksson
authors.forename: Benny
authors.initials: B
authors.lastname: Larsson
authors.forename: Michael Højby
authors.initials: MH
authors.lastname: Rasmussen
authors.forename: Anders
authors.initials: A
authors.lastname: Juul
authors.forename: Jens
authors.initials: J
authors.lastname: Bülow
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
mesh_terms: D015502:Absorptiometry, Photon; D000368:Aged; D000369:Aged, 80 and over; D001769:Blood / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D013006:Growth Hormone / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D006801:Humans; D006984:Hypertrophy; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000145:classification / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000473:pathology / Q000503:physiopathology*; D018995:Myosin Heavy Chains / Q000378:metabolism*; D010806:Physical Education and Training; D020033:Protein Isoforms / Q000378:metabolism; D019415:Torque; D014891:Weight Lifting
chemical_list: D020033:Protein Isoforms; D013006:Growth Hormone; D018995:Myosin Heavy Chains