Does metformin modify the effect on glycaemic control of aerobic exercise, resistance exercise or both?

Some previous studies suggested that metformin might attenuate the effects of exercise on glycaemia or fitness. We therefore examined whether metformin use influenced changes in glycaemic control, fitness, body weight or waist circumference resulting from aerobic and/or resistance training in people with type 2 diabetes participating in an exercise intervention trial. After a 4 week run-in period, participants from the Diabetes Aerobic and Resistance Exercise (DARE) trial were randomly assigned to 22 weeks of aerobic training alone, resistance training alone, combined aerobic and resistance exercise training or a waiting-list control group. Of the 251 randomised, 143 participants reported using metformin throughout the entire study period and 82 reported not using metformin at all. Compared with control, aerobic training led to a significant reduction in HbA(1c) in the metformin users (-0.57%, 95% CI -1.05, -0.10; -6.3 mmol/mol, 95% CI -11.5, -1.1) but not in the non-metformin users (-0.17, 95% CI -0.78, 0.43; -1.9 mmol/mol, 95% CI -8.5, 4.7). However, there were no significant differences in the changes in HbA(1c) (or fasting glucose) between metformin users and non-users in any of the exercise groups compared with control (p > 0.32 for all metformin by group by time interactions). Similarly, metformin did not affect changes in indicators of aerobic fitness, strength and body weight or waist circumference (pa parts per thousand yenaEuro parts per thousand 0.15 for all metformin by group by time interactions). Contrary to our hypothesis and to previous short-term studies, metformin did not significantly attenuate the benefits of exercise on glycaemic control or fitness.