Lots of transitions, collected trot along short side then push forward to a medium trot or try extended trot and then at short side come back to collected so on
I do serpentines up the hills but start at the walk to get the feel and do a lot of conditioning and trotting straight up hills, also lunging in the pasoa works for muscle building. hope this helps!!
Conditioning, lots of conditioning. Trot two minutes... canter 3 minutes... walk 5 minutes... gallop 2 minutes... and so on. I like to do this with music, so after a full song of trotting then a full song of cantering and so on.
Ground work like collecting trotting mainly and looks of sand work
Ground work, lots and lots of ground work. And if needed maybe add some grain that helps with building muscle.