I've never had any problem with my casting arm. I have had some problems with my back after a long day, but I doubt there is much to do about that.
My biggest concern is my ability to hike steep, long trails and still feel like fishing for a full day after the hike. I try to run two to three miles three times a week during the winter and usually will use the stair master during the summer. When I run, I try to use a route that will have an uphill climb. I find it makes a world of difference. As a bonus, it really helps on my occassional grouse hunting trip.