title: Insulin responsiveness in metabolic syndrome after eight weeks of cycle training.
abstract: BACKGROUND
  Insulin resistance in obesity is decreased after successful diet and exercise. Aerobic exercise training alone was evaluated as an intervention in subjects with the metabolic syndrome.
  
  
  METHODS
  Eighteen nondiabetic, sedentary subjects, 11 with the metabolic syndrome, participated in 8 wk of increasing intensity stationary cycle training.
  
  
  RESULTS
  Cycle training without weight loss did not change insulin resistance in metabolic syndrome subjects or sedentary control subjects. Maximal oxygen consumption (V·O 2max), activated muscle AMP-dependent kinase, and muscle mitochondrial marker ATP synthase all increased. Strength, lean body mass, and fat mass did not change. The activated mammalian target of rapamycin was not different after training. Training induced a shift in muscle fiber composition in both groups but in opposite directions. The proportion of type 2× fibers decreased with a concomitant increase in type 2a mixed fibers in the control subjects, but in metabolic syndrome, type 2× fiber proportion increased and type 1 fibers decreased. Muscle fiber diameters increased in all three fiber types in metabolic syndrome subjects. Muscle insulin receptor expression increased in both groups, and GLUT4 expression increased in the metabolic syndrome subjects. The excess phosphorylation of insulin receptor substrate 1 (IRS-1) at Ser337 in metabolic syndrome muscle tended to increase further after training in spite of a decrease in total IRS-1.
  
  
  CONCLUSIONS
  In the absence of weight loss, the cycle training of metabolic syndrome subjects resulted in enhanced mitochondrial biogenesis and increased the expression of insulin receptors and GLUT4 in muscle but did not decrease the insulin resistance. The failure for the insulin signal to proceed past IRS-1 tyrosine phosphorylation may be related to excess serine phosphorylation at IRS-1 Ser337, and this is not ameliorated by 8 wk of endurance exercise training.
authors.affiliation: 1Department of Internal Medicine, Quillen College of Medicine, East Tennessee State University, Johnson City, TN; 2Department of Exercise and Sport Science, Clemmer College of Education, East Tennessee State University, Johnson City, TN; and 3Department of Allied Health, College of Clinical and Rehabilitative Health, East Tennessee State University, Johnson City, TN.
authors.forename: Charles A
authors.initials: CA
authors.lastname: Stuart
authors.forename: Mark A
authors.initials: MA
authors.lastname: South
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Lee
authors.forename: Melanie P
authors.initials: MP
authors.lastname: McCurry
authors.forename: Mary E A
authors.initials: ME
authors.lastname: Howell
authors.forename: Michael W
authors.initials: MW
authors.lastname: Ramsey
authors.forename: Michael H
authors.initials: MH
authors.lastname: Stone
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D001823:Body Composition; D001835:Body Weight; D016022:Case-Control Studies; D005081:Exercise Therapy; D005260:Female; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D006801:Humans; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007333:Insulin Resistance; D008297:Male; D024821:Metabolic Syndrome / Q000378:metabolism* / Q000628:therapy*; D008875:Middle Aged; D025261:Mitochondrial Proton-Translocating ATPases / Q000378:metabolism; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000166:cytology / Q000378:metabolism; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D010101:Oxygen Consumption; D010766:Phosphorylation; D017856:Phosphotransferases (Phosphate Group Acceptor) / Q000378:metabolism; D011972:Receptor, Insulin / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D055815:Young Adult
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C495692:SLC2A4 protein, human; C546842:MTOR protein, human; D011972:Receptor, Insulin; D058570:TOR Serine-Threonine Kinases; C118888:AMP-dependent kinase (ATP-forming); D017856:Phosphotransferases (Phosphate Group Acceptor); D025261:Mitochondrial Proton-Translocating ATPases