The horse's physical development
All of us have heard the statement that proper dressage makes a horse more beautiful. If you're not sure if your training and/or lessons are successful, look at your horse. True, it takes time. Not forever, though! Your horse's physical development is a good check of whether or not your horse is really "on the bit" or "on the aids" (the preferred term).
Neck changes are often the most obvious. The neck should gradually become more arched and develop a crest, but the degree depends somewhat on whether you have a stallion, mare, or gelding. This can be noticeable even at rest. Over-developed under-neck muscles must be eliminated. Also, the neck should develop width from the base (in front of the withers) up and not from the ears down. The former indicates that the neck is stabilized between the shoulders. The latter indicates resistance in the poll. These horses also often "break" in the third vertebra instead of the poll.
Incorrect attempts at collection can result in a shortened, cramped neck, and the horse is then above the aids at the withers. In that case, the half-halts cannot go past that point, over the back, to the hind fetlock. The back becomes hollow, and this prevents "connection" and "throughness". If the horse's back is properly "up", the backbone should become less prominent as muscles develop along either side of it. Your saddle may fit better, too.
If the hind legs are active, they not only track up under the body, but also close the angles of the joints, resulting in a lowering of the hindquarters. The muscles that develop in the upper hind leg just above the gaskin are known as "breeches" because they look, from the rear, like the old-fashioned breeches with a "peg."
The muscles over the top of the croup should be smooth and long, not bunchy and overdeveloped. Likewise, there should be no "hunter bump" or peak. These unwanted changes mean the angles of the hind leg are not closing. If there is no lowering of the haunches, there is no relative elevation of the forehand. A straightened hind leg can pop you out of the saddle, too, and indicate that the hind legs are "out" or being "left behind". You want to develop a "body mover" as opposed to a "leg mover."
There should be an even and harmonious development of the horse's body which results in transforming some of the "pushing power" into "carrying power". This can be heard as well as seen. The horse no longer pounds the ground. A horse that is using itself properly is sounder, more comfortable (not at the expense of big movement), and more beautiful, too!
-- by Suzanne May