My newest harness is the Magic Marine MX2 and I lasted 2 minutes before the pain hit right on the L4,5/S1 joints. After online reading into sailing injuries etc I am looking at info on the Worrell XT, Ronstan PRO with a firm back support, Aquata Equipe XT and a UK harness from Forward Sail with its own integrated lumbar support. So there appear to be options there. Getting to trial those apart from the Ronstan here in Oz may be a bit hard but investigating further. First off am getting a weightlifters back brace to see if that helps.