Metformin is one of the most popular drugs for managing type 2 diabetes. Taking metformin alone reduces the risk of progression of type 2 diabetes 31%. On the other hand, having 150 minutes of exercise per week reduces the same risk by 58%. Scientists expected that combining both metformin and exercise will have a synergistic effect.
In one study, researchers chose adults over 60 years old and randomized them into two groups: the first group was taking placebo and exercising, and the second group was taking 1500-2000 mg/day of metformin and exercising. After 12 weeks, insulin sensitivity in the group taking placebo significantly increased. Interestingly, the insulin sensitivity did not worsen, at best (it improved in half of the participants and worsened in the other half).
There was one more interesting study. In the first group, participants did a 40-minute training daily for two weeks and their insulin sensitivity improved by 42%. Participants in the second group received 1700 mg/day of metformin for two weeks before the same 2-week training, and they have not experienced any positive effects of exercise. In a group receiving placebo, aerobic capacity measured as VO2max increased by 50% more than in the metformin group, and continuous glucose monitoring showed that the metformin group had constantly higher blood glucose levels (+10%). What was even more interesting is that muscle biopsy showed that patients taking metformin had a negative impact on mitochondrial processes. In short, metformin prevented all positive adaptations to physical activity that was performed by participants.
Although metformin may be useful for some people, at least for some short time, it negatively impacts all physical efforts and, actually, prevents metabolic health from improving.
Metformin prevents muscles from growing and recovering after strength training. It cancels the positive effects of muscle fiber tension. The muscle fiber does not thicken and does not become stronger.
The subjective Rate Of Perceived Exertion (RPE) increases when using metformin. It means that the usual working weight seems heavier when someone exercises while taking metformin.
If you have clients taking metformin and exercising, you may want to share this information with them, and potentially encourage them to discuss the possibility of getting off metformin with their medical doctor.
References:
Konopka, Adam R et al. “Metformin inhibits mitochondrial adaptations to aerobic exercise training in older adults.” Aging cell vol. 18,1 (2019): e12880. doi:10.1111/acel.12880
Long, Doug E et al. “Metformin to Augment Strength Training Effective Response in Seniors (MASTERS): study protocol for a randomized controlled trial.” Trials vol. 18,1 192. 26 Apr. 2017, doi:10.1186/s13063-017-1932-5
Jevtovic, Filip. “Combination of Metformin and Exercise in Management of Metabolic Abnormalities Observed in Type 2 Diabetes Mellitus.” Diabetes, metabolic syndrome and obesity : targets and therapy vol. 14 4043-4057. 16 Sep. 2021, doi:10.2147/DMSO.S328694