Volume of supervised exercise training impacts glycaemic control in patients with type 2 diabetes: a systematic review with meta-regression analysis

Supervised exercise programmes improve glycaemic control in type 2 diabetes, but training characteristics associated with reduction in HbA(1c) remain unclear. We conducted a systematic review with meta-regression analysis of randomised clinical trials (RCTs) assessing the association between intensity and volume of exercise training (aerobic, resistance or combined) and HbA(1c) changes in patients with type 2 diabetes. Five electronic databases were searched (1980-2012) to retrieve RCTs of at least 12 weeks' duration, consisting of supervised exercise training vs no intervention, that reported HbA(1c) changes and exercise characteristics. Two independent reviewers conducted study selection and data extraction. Twenty-six RCTs (2,253 patients) met the inclusion criteria. In multivariate analysis, baseline HbA(1c) and exercise frequency explained nearly 58% of between-study variance. Baseline HbA(1c) was inversely correlated with HbA(1c) reductions after the three types of exercise training. In aerobic training, exercise volume (represented by frequency of sessions) was associated with changes in HbA(1c) (weighted r = -0.64), while no variables were correlated with glycaemic control induced by resistance training. In combined training, weekly volume of resistance exercise explained heterogeneity in multivariate analysis and was associated with changes in HbA(1c) levels (weighted r = -0.70). Reduction in HbA(1c) is associated with exercise frequency in supervised aerobic training, and with weekly volume of resistance exercise in supervised combined training. Therefore, exercise volume is a major determinant of glycaemic control in patients with type 2 diabetes.