I blew out my L4 L5 at work in 2007 in 2008 I had an operation to fix it because nothing else worked I was only surfing in those days and it took almost a year to get back on the board and a mal too short board was to much still . I started kite surfing in 2010 no problems so far.
It just comes down to exercise and a positive mind. Lots of swimming helped a lot and heaps of core work in the gym and then lots of running on the beach .
Then in 2012 broke my foot kiting .
Six screws and a plate 8 months off the water .
Didn't have any problems with my back from the impact that broke my heal into six pieces .
Still kite surfing still loving it never going to stop !!!!