HeavyInt said..
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the only real fix is to fix the core (and not have any hard landings), impact kills backs, core strength exercises helps heaps.
Agree. I had a herniated disk in late 2012. You need time away (I didn't kite for 9 months), build and maintain core strength. I also dropped 15kg which helps.
My excercise plan is tough, maybe a bit too tough, I pulled a back mussel mid 2013, but the disks all held up.
BTW, I use a waist harness without issue.