title: Mechanisms underlying enhancements in muscle force and power output during maximal cycle ergometer exercise induced by chronic β2-adrenergic stimulation in men.
abstract: The study was a randomized placebo-controlled trial investigating mechanisms by which chronic β2-adrenergic stimulation enhances muscle force and power output during maximal cycle ergometer exercise in young men. Eighteen trained men were assigned to an experimental group [oral terbutaline 5 mg/30 kg body weight (bw) twice daily (TER); n = 9] or a control group [placebo (PLA); n = 9] for a 4-wk intervention. No changes were observed with the intervention in PLA. Isometric muscle force of the quadriceps increased (P ≤ 0.01) by 97 ± 29 N (means ± SE) with the intervention in TER compared with PLA. Peak and mean power output during 30 s of maximal cycling increased (P ≤ 0.01) by 32 ± 8 and 25 ± 9 W, respectively, with the intervention in TER compared with PLA. Maximal oxygen consumption (V̇o2max) and time to fatigue during incremental cycling did not change with the intervention. Lean body mass increased by 1.95 ± 0.8 kg (P ≤ 0.05) with the intervention in TER compared with PLA. Change in single fiber cross-sectional area of myosin heavy chain (MHC) I (1,205 ± 558 μm(2); P ≤ 0.01) and MHC II fibers (1,277 ± 595 μm(2); P ≤ 0.05) of the vastus lateralis muscle was higher for TER than PLA with the intervention, whereas no changes were observed in MHC isoform distribution. Expression of muscle proteins involved in growth, ion handling, lactate production, and clearance increased (P ≤ 0.05) with the intervention in TER compared with PLA, with no change in oxidative enzymes. Our observations suggest that muscle hypertrophy is the primary mechanism underlying enhancements in muscle force and peak power during maximal cycling induced by chronic β2-adrenergic stimulation in humans.
authors.affiliation: Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark; Department of Respiratory Research, Bispebjerg University Hospital, Copenhagen, Denmark;
authors.forename: Morten
authors.initials: M
authors.lastname: Hostrup
authors.affiliation: Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark; Department of Respiratory Research, Bispebjerg University Hospital, Copenhagen, Denmark;
authors.forename: Anders
authors.initials: A
authors.lastname: Kalsen
authors.affiliation: Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark; Department of Respiratory Research, Bispebjerg University Hospital, Copenhagen, Denmark;
authors.forename: Johan
authors.initials: J
authors.lastname: Onslev
authors.affiliation: Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark; Department of Respiratory Research, Bispebjerg University Hospital, Copenhagen, Denmark;
authors.forename: Søren
authors.initials: S
authors.lastname: Jessen
authors.affiliation: Department of Respiratory Research, Bispebjerg University Hospital, Copenhagen, Denmark;
authors.forename: Christoffer
authors.initials: C
authors.lastname: Haase
authors.affiliation: Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark;
authors.forename: Sajad
authors.initials: S
authors.lastname: Habib
authors.affiliation: Department of Sports Science and Biomechanics, University of Southern Denmark, Odense, Denmark; and Swedish Winter Sports Research Centre, Mid Sweden University, Sundsvall, Sweden.
authors.forename: Niels
authors.identifier: http://orcid.org/0000-0001-9060-4139
authors.initials: N
authors.lastname: Ørtenblad
authors.affiliation: Department of Respiratory Research, Bispebjerg University Hospital, Copenhagen, Denmark;
authors.forename: Vibeke
authors.initials: V
authors.lastname: Backer
authors.affiliation: Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark; jbangsbo@nexs.ku.dk.
authors.forename: Jens
authors.initials: J
authors.lastname: Bangsbo
mesh_terms: D018663:Adrenergic Agents / Q000494:pharmacology*; D000328:Adult; D001642:Bicycling / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D010807:Physical Endurance / Q000187:drug effects* / Q000502:physiology*; D052097:Quadriceps Muscle / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D055815:Young Adult
chemical_list: D018663:Adrenergic Agents; D009124:Muscle Proteins; D019344:Lactic Acid; D018995:Myosin Heavy Chains
keywords: Ca2+ handling; beta-adrenoceptor; contractile properties; doping; muscle growth