have you looked at the Cochrane library to see if there is a systematic review

Yes mam, I have tried to search the review in Cochrane library but i am unable to find it . Can you please give me the title of the paper or the author's name

Try Normand Boule and Malin SK. You may be able to find a few more going through their articles. 

My understanding is that one cannot regularly find a synergy here.

F.e., see: 

Eshghi SR, Bell GJ, Boulé NG. Effects of aerobic exercise with or without metformin on plasma incretins in type 2 diabetes.Can J Diabetes. 2013 ;37(6):375-380. 

You may get help from the papers under the following links

http://www.ncbi.nlm.nih.gov/pubmed/16855995

http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD002968.pub2/abstract?userIsAuthenticated=false&deniedAccessCustomisedMessage=

http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD002966.pub2/abstract

Metformin increases insulin-stimulated glucose transport in insulin-resistant human skeletal muscle.Apr 16, 2019

https://www.nature.com › ... › articles

Metformin acutely lowers blood glucose levels by inhibition of ...

What does metformin do to your body?

This study reveals several ways by which metformin and exercise therapies can affect each other. By increasing heart rate, metformin could lead to the prescription of lower exercise workloads. Furthermore, under the tested conditions, exercise interfered with the glucose-lowering effect of metformin.

https://www.ncbi.nlm.nih.gov › pmc

Metformin and Exercise in Type 2 Diabetes - PMC - NCBI

Research suggests metformin, a widely prescribed diabetes medication, may diminish the benefits of exercise when used in combination. In this study, however, metformin combined with exercise training, but not exercise alone, lowered proinsulin concentrations and increased insulin clearance in adults with prediabetes.Jul 18, 2017

https://journals.physiology.org › doi

Exercise training and metformin, but not exercise training alone ...