A few people have commented about how I shouldn't bulk up but just use weights for fitness.

Bones respond to the stresses placed on them. To attempt to build bone strength, they have to be stressed. To continue to stress them means increased weight. Increased weight leads to increased muscular strength and variable amounts of muscle growth.

At my age and without the use of steroids, it is unlikely that I will become the next Dorian Yates.

I would like to gain some muscular mass though. Even if I do gain some, I will be far away from Yates and other bodybuilders like him. The DEXA (bone scan) tech advised me not to lose weight. I think that gaining some muscle mass that comes along with increased muscular strength, hopefully indicating increased bone strength, would be a good thing.

Yesterday, I read about an exercise study where a (small) group of osteoporosis patients practiced yoga for two years and had increases in their DEXA scans. While the details of the study weren't clear, it was a good sign that BMD can be increased through exercise. That was the hypothesis tested in the study, but because the details weren't given, I am doubtful about the exercise and nutrition protocols used for the study and control groups. Either way, there apparently was an increase, so it can be done.

In my case, I had been practicing a sequence of "strengthening" yoga poses for a number of years until I was diagnosed with osteo, so that's another reason I'm doubtful of yoga and why I am pursuing something more vigorous to try to reverse the BMD loss. The cause of my osteo is unknown, but I know yoga didn't prevent it from showing up, so something else was needed.

I also read a paper earlier this week about astronaut BMD recovery. Astronauts in microgravity (i.e., in orbit around Earth) lose about 1% BMD / month. This paper summarized data on their post-mission recovery. The conclusion was that they recover 50% of the mission-related loss in 9 months to 3 years, but no information was given about what, if any, interventions (e.g., nutrition and exercise) they undertake upon return.