The dressage horse who retains his relaxation at the highest levels of collection is the ideal. He is dynamic and elastic, swinging, steady and beautiful to watch. The rider doesn’t have to push or work too hard. He just sits quietly because his horse is well balanced. Relaxation is not only physically beneficial for the horse’s muscles, tendons and bones, but it is also beneficial for his interior – for his heart. Relaxation is the first goal that we strive for from the beginning of the horse’s training. However, a lot can go wrong when the rider tries to collect his horse and make him more active and expressive….
When you look at some of the Grand Prix horses in the warm-up area of a horse show, you can be fairly sure that some of them [are] never really relaxed and stretched. As a result, the rider asks for collection, and the horse gets higher and shorter in the neck and tense in the back. He may show something that looks like cadence, but the horse is not lower behind with active hind legs and a swinging back.
Hubertus Schmidt, “Building Power In Relaxation”, Practical Horseman, September 2014