Horses did not evolve to be suited for riding. No matter how much we want to believe that this is exactly what horses are for (riding), they aren’t.

Don’t want to inject your horse’s joints? Fine, but the only way you will be able to keep your horse truly sound is by doing this:

Nevzorov Haute Ecole Journal # 3
Any time spent on the horse's back is answered by simple physiology.
1-15 min: particular sensations are absent
15-30 min: growing (until a certain limit) discomfort
After 30min, characterized by simple physiological analysis as "strong pain"
Anymore- Trauma

So this means that the rider should not be on the horses back more than 15minutes 3 times a week, and that is of correct riding.
Those sport horses that you see, the majority of them are lame. Sadly, very few people see it because the horses are evenly sound and/or the people have not been exposed to truly sound horses and therefore don’t know what to look for.
Remember: Thoroughbreds get hot, warmbloods get lazy. This just means that hotter breeds run away from the pain while the colder breeds stop due to the pain. This is the reason why race horses (Thoroughbreds, Arabians, and Quarter Horses) can’t really walk. They prance all the time, and take off quite often.
More to come: About Injections, Popular Myths, and Personal Cases