Moshe M. In the most recent Peter Attia podcast with Dr. Barzilai and Dr. Mannick, Dr. Barzilai mentioned that, at least for older people, metformin did not cause a loss of muscle function. He said that while the metformin group had less muscle mass growth, the function was actually the same. Dr. Barzilai also said that in this elderly population, metformin kept the young profile of muscle. And that at the end, maybe you had less muscle, but you had the same function, and you gained by metformin protecting 500 transcripts that are  aging transcripts. [These comments are mostly from Dr. Attia’s show notes. I listened to the whole 2 hour and sixteen minute podcast while gardening.]

@David H  Dave, I tried metformin about 5 years ago, and it reduced my testosterone by ~ 50%.  Calorie restriction does the same. In both cases my total T was below acceptable level as  even though I supplement with androderm. You can confirm this with google. Both  also increased my my cholesterol due to feedback loop. Suggest everyone  be careful as testosterone and  estradiol (due to to aromatization) are critical for preventing dementia, osteoporosis and  sarcopenia in seniors. I ceased both as result since I am almost 80 and continue to already supplement with androderm due to andropause.. 

I just did 25 chin ups and 26 pull ups this am. Don't need the adverse impacts of metformin at my age.

I also note that there is some opposition to metformin as It is thought to adversely impact mitochondria after long term use.