I know that hill work is good for her quarters and I can do that on a Saturday, and more often when it gets light in the summer, but what else can I do to build those muscles? Are transitions good?
Transitions are excellent! That is what I mainly do with all my horses, among other exercises.
Canter to walk (no trot), walk to canter (no trot), canter to halt, halt to canter, and rein back to canter. Before rein back, you need a good square full stop for more than 3 seconds, then rein back, and immediate canter continued.
These exercises will build muscles, and teach the horse to be obedient at the half stops you will need during a course.
There are many other exercises which will make the horse put hinds underneath body and lift forehands.
transitions are excelent indeed and might make your horse a bit hot (eager to go). other exercises are shoulder-in and everything from there (to pirouettes last): horse bend to side and innerhindleg needs to carry more weight. This also gives you the chance to strengten one side more than the other in case that is needed. When making small circles or turnings don't forget she HAS to use (lift) that inner leg as not to twist it. Transitions can also be made on a circle, if you keep the ritm and not go much faster. Be carefull and good luck Bronya!
