It has long been thought that exercise is good for bones because the stress stimulates the bones to become stronger. Heavier people generally have higher bone mineral density (BMD), presumably due to the higher stress put on their bones.
Some time ago, I was giving a talk and mentioned that exercise is good for bones. Someone asked if you need to exercise your upper body in order for bones in your upper body to benefit from exercise. I didn’t know the answer; it didn’t seem unreasonable to me that any exercise could stimulate increased BMD via hormones circulating throughout the entire body.
I finally got around to looking into it today. I found a number of abstracts of experiments and meta-analyses looking at whether exercise improves BMD. Most indicated that exercise does improve BMD in certain spots, especially the hip and spine.
I only found one study that compared upper body exercise to lower body exercise:
Winters-Stone KM, Snow CM. Site-specific response of bone to exercise in premenopausal women. Bone. 2006 Dec;39(6):1203-9. Epub 2006 Jul 28.
People who did upper and lower body exercise had more improvement in their lower back BMD compared to people who only did lower body exercise. Unfortunately, it appears that they didn’t measure the spine in the upper back or other upper body areas which would have been interesting information.
This is just one study and I don’t think it’s conclusive, but so far it appears that at least some of your bones will benefit from doing upper body resistance exercise in addition to lower body exercise.