Speyducer was at my house yesterday and, among other things, we discussed the earlier stages of shoulder damage vis-a-vis casting with two-handed rods.
A few of the things which emerged is that the long,(15' & +) rods - with modern, very fast recovery, have a heck of a kick when recovering their position at the stop. I had already found that these rods were simply too much for me and no longer use such rods.
It also came out that Ashley-Cooper who fished virtually every day of every season would go off down the river with several rods, graphite and bamboo, and use them all but for short spells of time and would also use every cast possible with switching of the upper hand from L to R. He argued that - especially older bodies - this spread the strain on tendons, muscles and joints as much as possible thus minimising the possibility of injury. I now do likewise but restrict myself to 3 rods of different characteristics and a handful of different casts (my lack of repetoire is responsible) and I can now fish at maximum distance - often in a howling gale - all day without too much post-fishing stiffness. This is a blessed relief after what I knew four years ago when I would fish a 151/2' Salar all day with both elbows in agony!!
The main point of this is that prevention is far far better than any cure, and to point to a possible method of fishing 2 handed rods with minimum risk. I have sold all of my 15' and longer rods other than a 16'2" Solstice and an old Diawia 16'6" (for really big copper tubes in very cold water.)