It’s been known for at least two decades that small electric currents in the micro amp range can speed up the healing of bone fractures. There was some research being done on this at the Houston Medical Center. Along the same lines, weight bearing exercise creates small piezoelectric currents in the bone, stimulating an increase in bone density.
This is what cold laser therapy and pulsed emf therapy does. Puts energy into cells that need it so that they can get their repair processes working again.