Once people hit the age 60, the decrease in muscle mass and strength happens on a much faster scale. There are several causes to this: A loss in the size and number of total muscle fibers, and primarily fast twitch as they're scarcely recruited in the retirees that lose them; changes in the physiological responses of the counter-activation of the antagonist muscles in sync with the agonist contraction; circulation of anabolic hormones in the blood declines; excitation-contraction process dulled, therefore making it require more stimulus for the same contraction, and then some minor reasons. Take home message being, "there's lots of things contributing to old people losing muscle."
Age is virtually always associated with a decline in use of muscles. That said, what do you think is causing the loss? So if that's the primary underlying cause, doesn't it seem fairly easy to reverse it? Progressive strength training in all people, particularly the older ones we're talking about here, will in fact do the trick. It will positively reverse neural adaptations, assist the agonist/antagonist contraction coupling, improve acute training-induced hormone circulation, and increase muscle cross-sectional area, affecting both fast and slow twitch fibers, obviously limiting or reversing the loss in muscle fiber size and count, and through all these factors, induce strength gains
, not just limit loss.
So if you're getting old, please get crackin' asap, because you don't have as much time as the rest of us. And realize that regardless of the fact that you're old, you're still a human being, so all the fundamental training principles that affect other human beings, affect you identically. So you can go after your fitness exactly like everyone else. My suggestion though: start slow. I don't need you having a stroke because of stuff I told you to do. So please start slow. Start with a walking and stretching routine for a month. Once that's comfortable, put in interval training on the bikes and other cardio equipment. After a month or so, when that's comfortable, begin to do some low back and abdominal work in addition to the interval cardio training. After another month, begin including some of the fundamental exercises. You follow? Aside from the rate at which you increase your intensity, everything else is the same. Okay, go nab grab yourself some healthiness.