Hi CollegeB. You posted a question about bone training. I'm not 100% sure that the information I will give are the answers you seek, or that my information will be absolutely correct, but here goes with what I have heard, read and learned.
You probably already know that bone density actually increases as the muscles are used/developed. Weight training is great for increasing bone strength/density as the use of the muscles with increasing weight causes the bone to build-up in order to support the changes in the muscle. Of course, the effectiveness of the bone development depends on diet quite a bit. I lift weights at least twice a week and I also have about three days a week where I do body weight exercises to strengthen and condition my muscles (push-ups, squats, martial arts). All that in the effort to not only get more physically fit, but to also decrease chances of osteoporsis in later life by building/maintaining good bone density. Don't know if you consider that bone training, I thought it kind of was so I included it.
In addition to the benefits of weight training, I've been told that bones will also build-up if they are exposed to very careful bruising which is a kind of bone conditioning. By "very careful bruising," I do not mean that a person should start throwing full-bore punches at a metal plate to jump into bone conditioning. That is a great way to completly ruin the joints. If a person wants to try to condition their bones in their knuckles, or any body-part used for striking, then he/she should find a hard surface and start lightly hitting it. The trainee should not hit so hard that he/she feels pain, and shouldn't hit thinking they have to have the bruising color to prove the bone is bruised. It is like any fitness training, discomfort is expected at the beginning, but it should not be pain and it should not be so bad that the trainee has to stop for long periods of recovery. It might sound weird, but a thick piece of a stripped log is great for this because it is round (no sharp edges or corners to risk painful injury) and it is very thick wood so it will take the punishment pretty well without punishing the trainee.
I buy the bone conditioning theory because I've been pegged (lightly punched) by my karate instructor who conditions his knuckles on a makiwara (hard striking target/surface) and this guy's knuckles are armor plated. He used a stripped log as a makiwara that he had cut to fit around the corner edge of one of his walls. That thing was probably orignally about 12 to 24 inches in diameter and most likely some kind of hardwood (poplar, hickory) as pine splinters very easily when struck. He would lightly hit it many times in a row to build up that bone armor, but never hard enough to harm the joints. I was feeling that bruise for about a month and that was just an accidental hit.
Those are the two methods I know best for bone training, weight training and very careful bruising. I hope this provided some of what you were looking for.