title: Physical activity intensity and type 2 diabetes risk in overweight youth: a randomized trial.
abstract: BACKGROUND
  The chronic effects of high-intensity endurance training on metabolic health outcomes in overweight adolescents remains poorly understood.
  
  
  OBJECTIVE
  To test the hypothesis that high-intensity endurance training (ET) is superior to moderate-intensity ET for improving risk factors for type 2 diabetes in overweight adolescents.
  
  
  METHODS
  In this randomized trial, 106 overweight and obese adolescents (15.2 years; 76% female; 62% Caucasian) were randomly assigned to high-intensity ET (70-85% of heart rate reserve, n=38), moderate-intensity ET (40-55% heart rate reserve; n=32) or control for 6 months (n=36). The primary and secondary outcome measures were insulin sensitivity assessed using a frequently sampled intravenous glucose tolerance test and hepatic triglyceride content with magnetic resonance spectroscopy. Exploratory outcomes were cardiorespiratory fitness, physical activity and MRI and dual x-ray absorptiometry-derived measures of adiposity.
  
  
  RESULTS
  The study had 96% retention and attendance was 61±21% and 55±24% in the high- and moderate-intensity ET arms. Intention-to-treat analyses revealed that, at follow-up, insulin sensitivity was not different between high-intensity (-1.0 mU kg(-1) min(-1); 95% confidence interval (CI): -1.6, +1.4 mU kg(-1) min(-1)) and moderate-intensity (+0.26 mU kg(-1) min(-1); 95% CI: -1.3, +1.8 mU kg(-1) min(-1)) ET arms compared with controls (interaction, P=0.97). Similarly, hepatic triglyceride at follow-up was not different in high-intensity (-1.7% fat/water (F/W); 95% CI: -7.0, +3.6% F/W) and moderate-intensity (-0.40% FW; 95% CI: -6.0, +5.3% F/W) ET compared with controls. Both high intensity (+4.4 ml per kg-FFM (fat-free mass) per minute; 95% CI: 1.7, 7.1 ml kg-FFM(-1) min(-1)) and moderate intensity (+4.4 ml kg-FFM(-1) min(-1); 95% CI: 1.6, 7.3 ml kg-FFM(-1) min(-1)) increased cardiorespiratory fitness, relative to controls (interaction P<0.001).
  
  
  CONCLUSIONS
  ET improves cardiorespiratory fitness among obese adolescents; however, owing to lack of compliance, the influence of exercise intensity on insulin sensitivity and hepatic triglycerides remains unclear.
authors.affiliation: Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.|Department of Pediatrics and Child Health, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.|Faculty of Kinesiology and Recreation Management, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Hay
authors.affiliation: Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.|Department of Pediatrics and Child Health, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Wittmeier
authors.affiliation: Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: A
authors.initials: A
authors.lastname: MacIntosh
authors.affiliation: Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.|Department of Pediatrics and Child Health, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: B
authors.initials: B
authors.lastname: Wicklow
authors.affiliation: Faculty of Kinesiology and Recreation Management, University of Manitoba, Winnipeg, Manitoba, Canada.|Health, Leisure and Human Performance Research Institute, Winnipeg, Manitoba, Canada.|Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.|Institute of Cardiovascular Sciences, St. Boniface Research Centre, Winnipeg, Manitoba, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Duhamel
authors.affiliation: Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.|Department of Pediatrics and Child Health, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: E
authors.initials: E
authors.lastname: Sellers
authors.affiliation: Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.|Department of Pediatrics and Child Health, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: H
authors.initials: H
authors.lastname: Dean
authors.affiliation: Faculty of Kinesiology and Recreation Management, University of Manitoba, Winnipeg, Manitoba, Canada.|Health, Leisure and Human Performance Research Institute, Winnipeg, Manitoba, Canada.
authors.forename: E
authors.initials: E
authors.lastname: Ready
authors.affiliation: Diabetes Research Group, Health Sciences Centre of Winnipeg, Winnipeg, Manitoba, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Berard
authors.affiliation: Faculty of Medical Rehabilitation, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Kriellaars
authors.affiliation: Diabetes Research Group, Health Sciences Centre of Winnipeg, Winnipeg, Manitoba, Canada.
authors.forename: G X
authors.initials: GX
authors.lastname: Shen
authors.affiliation: Faculty of Kinesiology and Recreation Management, University of Manitoba, Winnipeg, Manitoba, Canada.|Health, Leisure and Human Performance Research Institute, Winnipeg, Manitoba, Canada.|Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Gardiner
authors.affiliation: Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.|Department of Pediatrics and Child Health, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.|Faculty of Kinesiology and Recreation Management, University of Manitoba, Winnipeg, Manitoba, Canada.|Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: J
authors.initials: J
authors.lastname: McGavock
mesh_terms: D000293:Adolescent; D015992:Body Mass Index; D002170:Canada; D002320:Cardiovascular Physiological Phenomena; D003924:Diabetes Mellitus, Type 2 / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control; D005081:Exercise Therapy; D005260:Female; D006801:Humans; D007333:Insulin Resistance; D008297:Male; D010349:Patient Compliance; D063766:Pediatric Obesity / Q000097:blood / Q000150:complications / Q000503:physiopathology*; D010807:Physical Endurance; D010809:Physical Fitness; D055070:Resistance Training; D012307:Risk Factors; D016896:Treatment Outcome; D014280:Triglycerides / Q000032:analysis / Q000097:blood
chemical_list: D014280:Triglycerides