I'm guessing that if you do something to improve your health enough that it adds years to your life, the rest of your health should be improved as well.
Meaning, maybe standing also improves your back and you ache less in later years.
It's hard for me to imagine doing something that improves your life expectancy at the expense of some part of your body.
As a general principal, I would disagree with the position that it's not valid. Certainly some people who quit smoking late in life prolong a painful cancerous demise, however I would imaging the worst of the low-quality disabled years are often a result of the limited, desperate nature of the available potential life-saving treatments: radiation/chemotherapy, etc. A significant percentage of smokers quit late in life and avoid those extremely low-quality disabled life years. Also, it seems perspective typically changes as 'quality of life' decreases, generally resulting in the desire for continued respiration;-)
Meaning, maybe standing also improves your back and you ache less in later years.
It's hard for me to imagine doing something that improves your life expectancy at the expense of some part of your body.
This is massive speculation on my part.