Have the problems changed? In his book, written in the 1980’s, Reminisences of a Portuguese Rider, Nuno says: “Generally speaking, there is a tendency to break horses too quickly and too roughly, which results in irregularities of gait. How often does one see a sway back effect after the result of bad handling?”

“Horses are often forced too soon to extend the trot, gesticulating with the front legs with no thought for the necessary thrusting forward of the hind legs, leading to a concave back. It is different, of course, with a horse who has a naturally good extension and stays well balanced, this one can be pushed earlier in this pace.”

https://www.horsemagazine.com/thm/2021/03/nuno-oliveira-talks-about-competition-dressage/