Old != Frail

Old != Frail - these can be mutually exclusive adjectives, but it requires intervention. Image below is a great example of this. The active 40yr old and 70yr old have similar lean mass in the MRI scan, could even argue that the 70yr old has more, whilst the 74yr old sedentary man is showing a lot of muscle wastage which has obvious impact on his mobility and quality of life.

Sarcopenia is the natural loss of muscle mass as we age , and can even start in our mid-twenties. Roughly speaking, every 20yrs you can lose 1st (14lbs) of muscle mass. So even if you are careful with what you eat and drink, and weigh the same at 20, 40, 60 and 80, then you've likely replaced ~3st of lean mass with fat if you've lead a mostly sedentary lifestyle (desk job!), and it's that muscle mass loss and associated loss of strength that brings that word frail back into play.

To counter this, you chip into your physical pension with being active. As far as lean mass retention and/or growth goes, then resistance training is hands down the best method. It also brings other health benefits on the likes of osteoporosis (bone will also strengthen), blood pressure and blood sugars - bit of a read, but this has some good detail.

You may have experienced this is in a fashion,  if you or a someone you know has broken a limb, that then had a cast that covers the joint, taking it out of action for several weeks. The difference in muscle mass between the limbs when the cast is removed is striking, and can take several months for that to be regained.