OK. Back to the back/spine, muscle mass ... just wanted to add this.
I'm not sure what kinds of implants may be in the spine, if any. BUT- the vertebrae correspond to dermis in a precise way actually. Not sure what your own sensory awareness is re strength/weakness, muscle, sensation etc.
The C6, C7, C8 sections are only on the back, perception-wise, and run through the arms. You may be able to test which vertebrae yourself just by sensing out the hands...? Just a thought.
It's all interesting
marvel actually