muscle and strength lost

[manpwrxx]

At what age would people start losing muscle mass and strength caused by hormonal changes?

[derekpara]

I am a male 72 year old and have noticed that in the last year or two I have lost muscle mass, mainly from my legs and arms. There has also been a corresponding loss of strength. I notice this when I go to stand up from a kneeling position - I now need to use hand pressure on a nearby higher surface to regain my feet. My background is as a good club level swimmer and athlete for many years and a PE teacher until retirement at 65. I still go to the gym five times a week and am in good health. People remark on how fit I am. Hope this helps.