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Physical activity intensity and type 2 diabetes risk in overweight youth: a randomized trial
Hay J, Wittmeier K, MacIntosh A, Wicklow B, Duhamel T, Sellers E, Dean H, Ready E, Berard L, Kriellaars D, Shen GX, Gardiner P, McGavock J
International Journal of Obesity 2016 Apr;40(4):607-614
clinical trial
7/10 [Eligibility criteria: No; Random allocation: Yes; Concealed allocation: No; Baseline comparability: Yes; Blind subjects: No; Blind therapists: No; Blind assessors: Yes; Adequate follow-up: Yes; Intention-to-treat analysis: Yes; Between-group comparisons: Yes; Point estimates and variability: Yes. Note: Eligibility criteria item does not contribute to total score] *This score has been confirmed*

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. DESIGN AND 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 to 85% of heart rate reserve, n = 38), moderate-intensity ET (40 to 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 (-1.0mU/kg/min; 95% confidence interval (CI) -1.6 to +1.4mU/kg/min) and moderate-intensity (+0.26mU/kg/min; 95% CI -1.3 to +1.8mU/kg/min) 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 to +3.6% F/W) and moderate-intensity (-0.40% FW; 95% CI -6.0 to +5.3% F/W) ET compared with controls. Both high intensity (+4.4ml per kg-FFM (fat-free mass) per minute; 95% CI 1.7 to 7.1ml/kg-FFM/min) and moderate intensity (+4.4ml/kg-FFM/min; 95% CI 1.6 to 7.3ml/kg-FFM/min) 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.

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