We too believe that it starts with optimum nutrition.
Then comes aerobic conditioning. Once aerobic conditioning is in place, we build muscle and strength on top of that. Never the other way around. An aerobically conditioned animal will be less prone to injury.
I would accomplish this first with distance work, like driving a low drag cart, at the trot, over distance and primarily on level ground. After a period of this to build sufficient aerobic capacity, I would slowly shift to more hill work which will isolate and further build the rear half of the horse.
The layers of the onion, in order, would be.
1) superb nutrition
2) aerobic conditioning
3) strength training
By attending to aerobic conditioning first, you will develop strength with endurance. If you don't and jump directly to the strength exercise, you risk potential injury to the horse, will never build optimum strength and whatever strength you manage to build will have no staying power.
I also believe that you should find the most enjoyable ways for the horse to accomplish this task. Never miss a chance to capture the mind and heart of your horse in whatever endeavor you choose.
We FINALLY have sunny weather and are planting garden!
Bb
Graham Carriage Works
www.grahamcarriageworks.com