title: Two weeks of reduced activity decreases leg lean mass and induces "anabolic resistance" of myofibrillar protein synthesis in healthy elderly.
abstract: BACKGROUND
  Alterations in muscle protein metabolism underlie age-related muscle atrophy. During periods of muscle disuse, muscle protein synthesis is blunted, and muscle atrophy occurs in young and old. The impact of a short reduction in physical activity on muscle protein metabolism in older adults is unknown.
  
  
  OBJECTIVE
  The aim of this study was to investigate the impact of 14 days of reduced daily steps on fasted and fed-state rates of myofibrillar protein synthesis (MPS) to provide insight into the mechanisms for changes in muscle mass and markers of metabolic health.
  
  
  METHODS
  Before and after 14 days of reduced daily step-count, 10 healthy older adults (age, 72 ± 1 y) underwent measures of insulin sensitivity, muscle strength, physical function, and body composition. Using a primed constant infusion of L-[ring-(13)C6]phenylalanine with serial muscle biopsies, basal, postabsorptive, and postprandial rates of MPS were determined before and after the 14-day intervention.
  
  
  RESULTS
  Daily step-count was reduced by approximately 76% to 1413 ± 110 steps per day. Leg fat-free mass was reduced by approximately 3.9% (P < .001). Postabsorptive insulin resistance was increased by approximately 12%, and postprandial insulin sensitivity was reduced by approximately 43% after step reduction (P < .005). Concentrations of TNF-α and C-reactive protein were increased by approximately 12 and 25%, respectively, after step reduction (P < .05). Postprandial rates of MPS were reduced by approximately 26% after the intervention (P = .028), with no difference in postabsorptive rates.
  
  
  CONCLUSIONS
  The present study demonstrates that 14 days of reduced steps in older adults induces small but measurable reductions in muscle mass that appear to be underpinned by reductions in postprandial MPS and are accompanied by impairments in insulin sensitivity and systemic inflammatory markers and postprandial MPS.
authors.affiliation: Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1.
authors.forename: Leigh
authors.initials: L
authors.lastname: Breen
authors.forename: Keith A
authors.initials: KA
authors.lastname: Stokes
authors.forename: Tyler A
authors.initials: TA
authors.lastname: Churchward-Venne
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Moore
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Baker
authors.forename: Kenneth
authors.initials: K
authors.lastname: Smith
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Atherton
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Phillips
mesh_terms: D000368:Aged; D000596:Amino Acids / Q000097:blood; D001786:Blood Glucose / Q000032:analysis; D001823:Body Composition; D002097:C-Reactive Protein / Q000032:analysis; D004032:Diet; D004734:Energy Metabolism; D015444:Exercise; D005260:Female; D006801:Humans; D007333:Insulin Resistance; D007866:Leg; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis*; D009210:Myofibrils / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism
chemical_list: D000596:Amino Acids; D001786:Blood Glucose; D009124:Muscle Proteins; D002097:C-Reactive Protein; D038762:Ribosomal Protein S6 Kinases, 70-kDa