Well after two months in Peru and Chamonix, I definitely feel fitter than any time in the last decade or two. I have dropped at least a dozen pounds, while exercise volume, vertical, and intensity are all up ... HOWEVER I still do not do any regular strength training.
Corrine Malcolm - former biathlete and now big time ultra runner - spells it all out clearly in the article linked below. My daughter admonished me about sarcopenia several years ago, while she was taking an exercise physiology class at St. Paul's. I guess, loss of muscle mass while you age is real. So, I better get a program together.