A short back is a sign of strength, it is associated with a short wide loin, and provided the back is long enough for the saddle, the broad general statement may be made that it cannot be too short.

A long back is a weak back, it is associated with long weak loins and flat ribs, and its muscles are usually poorly developed.

High withers
When excessively high it is not uncommon to find the back hollow, and such a one is unfit to carry weight under military conditions.  High withers are always lean, narrow and razor like; the horse that possesses them is always in danger of injury for, as we have previously mentioned, the ridge of the back, which includes the withers, is perfectly incapable of sustaining pressure.

Low withers
  A wide wither is nearly as troublesome as a high one, not for the reason that it gets pressed upon, but owing to the fact that it is liable to be pinched.

Hollow backs
Hollow backs are associated with high withers and high loins.  It is a useless back for a military horse, as owing to its curve the saddle is unable to get a level bed on the back, and only the front and rear extremities bear on the back, with the result that injury follows.

Wide backs
Wide backs are those which possess a good arch to the ribs and afford a good bed for the saddle to rest on; it is an essential formation for a soldier’s horse.

Narrow backs
There is very little bearing surface for the saddle, and what back there is has a slope like the roof of a house, while the sides are flat. A flat-sided horse, besides carrying his saddle badly, is deficient in stamina and soon succumbs to fatigue.