title: Leucine partially protects muscle mass and function during bed rest in middle-aged adults.
abstract: BACKGROUND
  Physical inactivity triggers a rapid loss of muscle mass and function in older adults. Middle-aged adults show few phenotypic signs of aging yet may be more susceptible to inactivity than younger adults.
  
  
  OBJECTIVE
  The aim was to determine whether leucine, a stimulator of translation initiation and skeletal muscle protein synthesis (MPS), can protect skeletal muscle health during bed rest.
  
  
  METHODS
  We used a randomized, double-blind, placebo-controlled trial to assess changes in skeletal MPS, cellular signaling, body composition, and skeletal muscle function in middle-aged adults (n = 19; age ± SEM: 52 ± 1 y) in response to leucine supplementation (LEU group: 0.06 g ∙ kg(-1) ∙ meal(-1)) or an alanine control (CON group) during 14 d of bed rest.
  
  
  RESULTS
  Bed rest decreased postabsorptive MPS by 30% ± 9% (CON group) and by 10% ± 10% (LEU group) (main effect for time, P < 0.05), but no differences between groups with respect to pre-post changes (group × time interactions) were detected for MPS or cell signaling. Leucine protected knee extensor peak torque (CON compared with LEU group: -15% ± 2% and -7% ± 3%; group × time interaction, P < 0.05) and endurance (CON compared with LEU: -14% ± 3% and -2% ± 4%; group × time interaction, P < 0.05), prevented an increase in body fat percentage (group × time interaction, P < 0.05), and reduced whole-body lean mass loss after 7 d (CON compared with LEU: -1.5 ± 0.3 and -0.8 ± 0.3 kg; group × time interaction, P < 0.05) but not 14 d (CON compared with LEU: -1.5 ± 0.3 and -1.0 ± 0.3 kg) of bed rest. Leucine also maintained muscle quality (peak torque/kg leg lean mass) after 14 d of bed-rest inactivity (CON compared with LEU: -9% ± 2% and +1% ± 3%; group × time interaction, P < 0.05).
  
  
  CONCLUSIONS
  Bed rest has a profoundly negative effect on muscle metabolism, mass, and function in middle-aged adults. Leucine supplementation may partially protect muscle health during relatively brief periods of physical inactivity. This trial was registered at clinicaltrials.gov as NCT00968344.
authors.affiliation: Division of Rehabilitation Sciences, Departments of Nutrition and Metabolism.
authors.forename: Kirk L
authors.initials: KL
authors.lastname: English
authors.affiliation: Division of Rehabilitation Sciences, Departments of.
authors.forename: Joni A
authors.initials: JA
authors.lastname: Mettler
authors.affiliation: Physical Therapy, and.
authors.forename: Jennifer B
authors.initials: JB
authors.lastname: Ellison
authors.affiliation: Division of Rehabilitation Sciences, Departments of.
authors.forename: Madonna M
authors.initials: MM
authors.lastname: Mamerow
authors.affiliation: Division of Rehabilitation Sciences, Departments of.
authors.forename: Emily
authors.initials: E
authors.lastname: Arentson-Lantz
authors.affiliation: Internal Medicine, University of Texas Medical Branch, Galveston, TX; and.
authors.forename: James M
authors.initials: JM
authors.lastname: Pattarini
authors.affiliation: Office of Biostatistics, Universities Space Research Association, Houston, TX.
authors.forename: Robert
authors.initials: R
authors.lastname: Ploutz-Snyder
authors.affiliation: Internal Medicine, University of Texas Medical Branch, Galveston, TX; and.
authors.forename: Melinda
authors.initials: M
authors.lastname: Sheffield-Moore
authors.affiliation: Division of Rehabilitation Sciences, Departments of Nutrition and Metabolism, djpaddon@utmb.edu.
authors.forename: Douglas
authors.initials: D
authors.lastname: Paddon-Jones
mesh_terms: D015502:Absorptiometry, Photon; D001510:Bed Rest / Q000009:adverse effects*; D001707:Biopsy, Needle; D001823:Body Composition; D002247:Carbon Isotopes; D019587:Dietary Supplements / Q000009:adverse effects; D004311:Double-Blind Method; D005080:Exercise Test; D005260:Female; D006801:Humans; D007930:Leucine / Q000009:adverse effects / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D024510:Muscle Development; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D009133:Muscular Atrophy / Q000209:etiology / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D010101:Oxygen Consumption; D015398:Signal Transduction; D051598:Whole Body Imaging
chemical_list: D002247:Carbon Isotopes; D009124:Muscle Proteins; D007930:Leucine
keywords: atrophy; dietary supplementation; nutrition; physical inactivity; skeletal muscle protein synthesis