Found this article on exercise and age related muscle loss though I suspect that here on the 50+ forum, it will be preaching to the choir.
Intro paragraphs below, you can read the entire article here (link)
80-Year Olds With 40-Year Old Muscle Mass - What's Going On?
By Dr. Mercola
Increasing physical frailty as you age is commonly accepted as "a fact of life."
Until recently, most studies showed that after the age of 40, people typically lose eight percent or more of their muscle mass with each passing decade.
But newer research suggests that this is not a foregone conclusion.
One recent study of 40 competitive runners, cyclists, and swimmers, ranging in age from 40 to 81, found no evidence of deterioration -- the athletes in their 70s and 80s had almost as much thigh muscle mass as the athletes in their 40s.
Quoted in the New York Times, Dr. Vonda Wright, who oversaw the study, said:"We think these are very encouraging results…
They suggest strongly that people don't have to lose muscle mass and function as they grow older.
The changes that we've assumed were due to aging and therefore were unstoppable seem actually to be caused by inactivity.
And that can be changed."
Other recent studies have had similar results. For example, in an animal study from last year, elderly sedentary rats put on a running program developed new satellite cells after 13 weeks. These cells are specialized stem cells known to repair and build muscle tissue