In addition to the exercise advice offered by others, take a closer look at your horse’s diet. Some years ago, I attended a seminar at which an equine nutritional expert stated that, contrary to popular belief, “proteins don’t build muscle, minerals do”. I’ve seen huge and rapid positive changes in several horses with various problems, with the only change being an excellent mineral supplement (my favorite is Hiland’s Big Sky). The same expert advised against ever offering “treat-type/flavored” minerals free choice.
Consider having your horse evaluated by an equine chiropractor/body worker to make sure that spinal misalignment/chronic cramping isn’t contributing to your problems. Does your horse bend/flex/turn easily to both sides? Can your horse comfortably perform barefoot (if not, check out a trimming specialist)? I (as a barefoot trimmer) have seen some strange conformation issues resolve in short months when such issues are successfully addressed.
Final suggestion–make sure you feed your horse at ground level to help with the ewe neck thing. Feeding higher (especially with hay nets) does not keep your horse’s head/neck in a normal grazing position and can contribute to development of ewe neck over time. Perhaps lots of time spent confined to a stall resulted in what you’re seeing–nothing better for a horse’s body/mind than 24/7 turnout with friends!