Riding round, lunge work with lots of gait transitions, cavalletis, and lots of extra feed! I use beet pulp and it does a great job adding bulk.
Do a lot of stretching and getting round. Also so feeds r great too!
Add a scoop of rice bran.
Yeah give him plenty of feed with protein content and work him hard like galloping and maybe a bit of cross-country
Gridwork, cavaletti, lots of lunging and circling. Try lateral work and lots of trotting :)
Trot poles, walk/trot, trot/canter transitions and spiral work helped my older thoroughbred
If you have a lot of poles and/or cavaletti available, try starting with a row of 6-8 ground trotting poles, adding a pole when it is going well. up to 10 or 12 in a row. After a week or two, start raising some poles on the side altering left and right. When your horse has no difficulty anymore, try making it into a half circle with ground poles. When that is going well, try raising those as well. You can also try to leg yield on the straight row of poles, it hrlped my horse with keeping its rhythm!
I try to do this at least twice a week, it helps with coordination and strength. Just don't try to add/raise poles too fast.
You can also watch the Horsephysio videos, those have a lot of variation with trot or canter poles!
belly lifts & pelvic tilts
Long and low works well when warming up.
Trot poles work pretty great, but otherwise changing feed worked well for my boy! Adding a couple scoops of crushed weetbix or a scoop of Cool + works incredibly!