title: Strength exercise improves muscle mass and hepatic insulin sensitivity in obese youth.
abstract: BACKGROUND
  Data on the metabolic effects of resistance exercise (strength training) in adolescents are limited.
  
  
  OBJECTIVE
  The objective of this study was to determine whether a controlled resistance exercise program without dietary intervention or weight loss reduces body fat accumulation, increases lean body mass, and improves insulin sensitivity and glucose metabolism in sedentary obese Hispanic adolescents.
  
  
  METHODS
  Twelve obese adolescents (age = 15.5 ± 0.5 yr, body mass index = 35.3 ± 0.8 kg·m; 40.8% ± 1.5% body fat) completed a 12-wk resistance exercise program (two times 1 h·wk, exercising all major muscle groups). At baseline and on completion of the program, body composition was measured by dual-energy x-ray absorptiometry, abdominal fat distribution was measured by magnetic resonance imaging, hepatic and intramyocellular fat was measured by magnetic resonance spectroscopy, peripheral insulin sensitivity was measured by the stable-label intravenous glucose tolerance test, and hepatic insulin sensitivity was measured by the hepatic insulin sensitivity index = 1000/(GPR × fasting insulin). Glucose production rate (GPR), gluconeogenesis, and glycogenolysis were quantified using stable isotope gas chromatography/mass spectrometry techniques.
  
  
  RESULTS
  All participants were normoglycemic. The exercise program resulted in significant strength gain in both upper and lower body muscle groups. Body weight increased from 97.0 ± 3.8 to 99.6 ± 4.2 kg (P < 0.01). The major part (∼80%) was accounted for by increased lean body mass (55.7 ± 2.8 to 57.9 ± 3.0 kg, P ≤ 0.01). Total, visceral, hepatic, and intramyocellular fat contents remained unchanged. Hepatic insulin sensitivity increased by 24% ± 9% (P < 0.05), whereas peripheral insulin sensitivity did not change significantly. GPR decreased by 8% ± 1% (P < 0.01) because of a 12% ± 5% decrease in glycogenolysis (P < 0.05).
  
  
  CONCLUSIONS
  We conclude that a controlled resistance exercise program without weight loss increases strength and lean body mass, improves hepatic insulin sensitivity, and decreases GPR without affecting total fat mass or visceral, hepatic, and intramyocellular fat contents.
authors.affiliation: Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Gert-Jan
authors.initials: GJ
authors.lastname: Van Der Heijden
authors.forename: Zhiyue J
authors.initials: ZJ
authors.lastname: Wang
authors.forename: Zili
authors.initials: Z
authors.lastname: Chu
authors.forename: Gianna
authors.initials: G
authors.lastname: Toffolo
authors.forename: Erica
authors.initials: E
authors.lastname: Manesso
authors.forename: Pieter J J
authors.initials: PJ
authors.lastname: Sauer
authors.forename: Agneta L
authors.initials: AL
authors.lastname: Sunehag
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000293:Adolescent; D005260:Female; D006801:Humans; D007328:Insulin / Q000502:physiology*; D008099:Liver / Q000378:metabolism*; D008297:Male; D009132:Muscles / Q000502:physiology*; D009765:Obesity; D055070:Resistance Training
chemical_list: D007328:Insulin