How exactly does vibration training affect bone density?
There are 3 ways that vibration training/therapy can affect your bone density, not just one.
The weight you carry around with you on a daily basis places your bones under pressure which is equivalent to 1G ( 1 x gravity ). This pressure is registered in the bone through Osteoblasts, a mononucleate cell that’s sole job is to help you create more bone tissue, but only if needed. The more weight you carry around with you dictates how strong your bones need to be which is why heavier people don’t get osteoporosis.
By creating a hyper-gravity situation, such as a vibration training platform coming quickly up underneath you, your body just for a split second becomes very heavy (on most standard units 6 times your own weight). This sudden g-load excites those osteoblasts and they create a very strong signal, hence more bone is built to accommodate the extra weight your body thinks it is carrying.
A muscle contracts which causes pressure on the supporting local bone structure. This effectively “bends” the bone and gets those osteoblasts excited again. This is a very local way of building bone density as only the bone being bent will be affected. However, by going into various workout poses on a training platform, the strong involuntary reflexes caused will effectively replicate a good weight training program. This in turn also creates more muscle mass which creates an even stronger contraction next time. Therefore, an upward spiral of stronger muscle which equals stronger bones which equals stronger muscle is set in motion.
Note: Again here pressure is the key. Think about this, doing a bicep curl without a weight in your hand will not create muscle or bone, so a simple contraction is not good enough.
This is the theory that none of the experts believe yet, so I will tell you about it and then let you decide. A basic engineering principle is that vibration causes a disturbance in all material. Some can absorb this for long periods of time and still function such as rubber. Other material that is more solid and inflexible like steel can be fractured quite easily. It is important to note that vibration alone can affect a change in a materials composition. No engineered materials remain static under the influence of vibration. Even rubber will eventually get hard and crack. Nanotechnology and other engineering advancements will take care of this problem eventually, but it will only be trying to replicate what nature already does.
In the human body, when that same energy which disturbs and separates non organic molecules is used to excite the osteoblasts, they do the only thing they know how to do, create more bone. After all, a cell does not differentiate between energy sources the last time I checked, force is force is force.