strong bones for a longer life
The more I learn about bones the more interesting they become (thank you to Nicholas Taleb and Antifragile). What fascinates me is the hormone feedback loop between bones and the rest of our bodies. There has been some accepted thinking that says that aging causes weak bones, perhaps brought on by hormones or lack thereof, especially in menopause. But it seems as though the reverse is also true: lack of bone density causes aging, metabolic disorders, diabetes and hormone issues. See the work of Gerard Karsenty. Strong bones, besides keeping us from breaking apart, make for a better and longer life. We humans are complicated, and so many elements of comfortable modern life are not in our best, most healthy interest.
There is some dispute over how much bone density is affected by loading. My opinion is that every biological system I have ever encountered will either strengthen or break when put under stress. I see no reason to believe that bones are evolutionary outliers. Of course any loading, any exercise, is better than none. Walking is fine exercise, and I make sure to walk a good number of steps every day as recorded on my iPhone. I also am a big believer in lifting heavy weight. The thing to keep in mind is that what ever we do or don’t to ourselves is most likely going to have a systemic impact rather than a simple isolated one.