To what extent can a good exercise programme help to recover lost muscle in people over 70 who, while very fit and active, have not exercised regularly in earlier years?
A proper exercise routine, including strength training, can be extremely beneficial and helpful to anyone, including the elderly. You should always consult your physician before beginning an exercise routine to see if you are healthy enough to perform it, especially if you have heart, lung, or other ailments.
"Geriatric Times" published an interesting article on this in 2005.
From the Guardian:
I looked at myself in the mirror one day, and saw an old man. I was overweight, my posture was terrible and there was skin hanging off me where muscle used to be. I looked like a wreck. I started to consider the fact that I was probably going to die soon. I knew I was supposed to slow down, but I'm vain. I missed my old body and wanted to be able to strut across the beach, turning heads.
I was already rowing six times a week, and there didn't seem any harm in pushing myself a bit harder to rebuild my muscles. So in my late-80s I joined a bodybuilding club.
Everything I learned was tailored to help my body cope with old age. I took up judo to teach me how to fall properly. My circulation and posture improved, and I was told that there was a chance more muscle mass could protect my brain from Alzheimer's. I stopped thinking about dying. As I approached 90, my focus was on getting my body back.
[At] last year's event in Germany, I triumphed, scoring higher than any contestant in any age category for my 57 dips, 61 chin-ups, 50 push-ups and 48 abdominal crunches, each in 45 seconds. As I'm over 70, they did make allowances – I could do the push-ups on my knees, for example – but I proved I wasn't past it.
He had an athletic past, but as mentioned elsewhere, the science shows that any physical activity, particularly balance, strength, and mobility training, is of particular benefit for geezers.