title: Increased skeletal muscle capillarization after aerobic exercise training and weight loss improves insulin sensitivity in adults with IGT.
abstract: OBJECTIVE
  Transcapillary transport of insulin is one determinant of glucose uptake by skeletal muscle; thus, a reduction in capillary density (CD) may worsen insulin sensitivity. Skeletal muscle CD is lower in older adults with impaired glucose tolerance (IGT) compared with those with normal glucose tolerance and may be modifiable through aerobic exercise training and weight loss (AEX+WL). We tested the hypothesis that 6-month AEX+WL would increase CD to improve insulin sensitivity and glucose tolerance in older adults with IGT.
  
  
  METHODS
  Sixteen sedentary, overweight-obese (BMI 27-35 kg/m2), older (63 ± 2 years) men and women with IGT underwent hyperinsulinemic-euglycemic clamps to measure insulin sensitivity, oral glucose tolerance tests, exercise and body composition testing, and vastus lateralis muscle biopsies to determine CD before and after 6-month AEX+WL.
  
  
  RESULTS
  Insulin sensitivity (M) and 120-min postprandial glucose (G120) correlated with CD at baseline (r = 0.58 and r = -0.60, respectively, P < 0.05). AEX+WL increased maximal oxygen consumption (VO2max) 18% (P = 0.02) and reduced weight and fat mass 8% (P < 0.02). CD increased 15% (264 ± 11 vs. 304 ± 14 capillaries/mm(2), P = 0.01), M increased 21% (42.4 ± 4.0 vs. 51.4 ± 4.3 µmol/kg FFM/min, P < 0.05), and G120 decreased 16% (9.35 ± 0.5 vs. 7.85 ± 0.5 mmol/L, P = 0.008) after AEX+WL. Regression analyses showed that the AEX+WL-induced increase in CD independently predicted the increase in M (r = 0.74, P < 0.01) as well as the decrease in G120 (r = -0.55, P < 0.05).
  
  
  CONCLUSIONS
  Six-month AEX+WL increases skeletal muscle CD in older adults with IGT. This represents one mechanism by which AEX+WL improves insulin sensitivity in older adults with IGT.
authors.affiliation: Corresponding author: Steven J. Prior, sprior@grecc.umaryland.edu.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Prior
authors.forename: Jacob B
authors.initials: JB
authors.lastname: Blumenthal
authors.forename: Leslie I
authors.initials: LI
authors.lastname: Katzel
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Goldberg
authors.forename: Alice S
authors.initials: AS
authors.lastname: Ryan
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001786:Blood Glucose / Q000378:metabolism; D001823:Body Composition / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005260:Female; D015309:Glucose Clamp Technique; D018149:Glucose Intolerance / Q000503:physiopathology*; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology*; D008297:Male; D055806:Microvessels / Q000502:physiology; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000098:blood supply*; D018919:Neovascularization, Physiologic; D009765:Obesity / Q000503:physiopathology*; D050177:Overweight / Q000503:physiopathology; D010101:Oxygen Consumption / Q000502:physiology; D015431:Weight Loss / Q000502:physiology
chemical_list: D001786:Blood Glucose; D007328:Insulin