Acute effect of metformin on exercise capacity in active males

Aim: Physical activity and metformin are often used concomitantly in the treatment of diabetes, even though little is known about possible interactions between these treatment modalities. This study was designed to examine the acute effect of metformin on oxygen consumption and lactate concentration during exercise. Methods: Eleven healthy, active men [mean ± s.d.: age = 29.9 ± 3.7 years; body mass index = 25.2 ± 2.8 kg/m²; maximal oxygen consumption (VO_2max) = 53.5 ± 8.9 ml/kg/min] completed a randomized, double-blind, placebo-controlled, crossover study. The testing protocol consisted of a standardized breakfast with metformin (1000 mg) or placebo. Three hours after breakfast, participants underwent a graded maximal exercise test on a cycle ergometer. Approximately 30 min after this exercise test, participants cycled continuously at an intensity below their ventilatory threshold for 45min (mean exercise intensity = 69 ± 5.5% of VO_2max). Results: During the graded exercise test, average oxygen consumption was higher for the metformin condition (2.9 vs. 2.8l/min, p = 0.04); however, there was no treatment effect on VO_2max or ventilatory threshold. During continuous exercise, lactate was lower for the metformin condition (4.7 vs. 5.4 mmol/l, p = 0.05). Following a standardized lunch, glucose concentrations were lower in the metformin compared with the placebo condition (5.8 vs. 6.4mmol/l, p = 0.04). Conclusion: A single dose of metformin does not acutely influence maximal oxygen consumption or ventilatory threshold in healthy active males. The lower lactate concentration observed during continuous exercise with metformin was an unexpected finding considering that, in the resting state, metformin has been previously associated with a modest increase in lactate concentrations.