This should be my mantra, your mantra: "The one that is supposed to be your best friend, your physical body, will become your worst enemy. Then you will have to live with your worst enemy." Remember, you will have to live with your worst enemy. Who wants to live with your worst enemy?
Physical fitness is of paramount importance. Do whatever exercise you want to, as long as you do something. I take daily at least two hours' exercise, sometimes two and a half, sometimes three. Usually, I do it at three different times during the day. Even at night, before I go to bed, I have some special exercises that I take.
Only my two poor knees are not my friends. Otherwise, the rest of my body is my very good friend.