Wouldn't it be wonderful if you could tell what gait a horse prefers by looking at his bone structure? To choose the perfect individual for a specific gaited breed, you could simply select the one with right proportions for that gait. Think how simple breeding and training would be!
Seductive as the thought may be, conformation can offer only part of the answer when it comes to the question of a horse's gait preference. A horse moves in any gait as a result of the combination of his bone structure, muscle development, and nerve patterns. He can work only within the limits of his physical ability. It's up to us to understand what our own individual horses are capable of, and to keep them sound and moving smoothly on the trail.
Bone vs. Muscle
Some types of bone structure predispose a horse to certain body positions, and those body positions, in turn, incline a horse to certain gaits.
However, a horse can modify his basic body position by using his muscles. He may inherit a particular bone structure, but what he does with it depends on his physical condition and his nervous-system development. This is true both of the characteristics that incline to certain gaits and to others that affect the quality of those gaits.
So, is bone structure a good indication of a preferred gait? There are obvious differences in bone structure between gaited and good nongaited horses, and additional subtle variations among the gaited breeds.
They may not correlate 100 percent to the gaits of choice of these horses, but they can give a good idea of whether an individual is capable of a particular easy gait and the style in which he will perform it. Conformation isn't the sole determinant of gait, but it is a major contributing factor.
Frame and Gait
Anyone who's ridden both gaited and nongaited horses in a light saddle or bareback eventually discovers that the way the horse's back feels changes from gait to gait. The noticeable variations in the back are a direct reflection of the body position or "frame" the horse uses in each gait. This position ranges from extremely hollow in the hard pace to extremely round, or basculed, in the collected trot.
Although some horses will trot in a hollow position, none will pace in a rounded one. A horse physically can't work in an easy gait with a rounded frame - that is, a sustained downward flexion of the lumbosacral junction in the lower spine, a raised back, increased flexion of all the joints in the hind legs (hip, stifle, hock, hind fetlock) and a raised root of the neck at the withers (i.e., in collection). He may work in a shortened frame, as does a racking horse, but he won't achieve the same frame as a basculed horse. If he did, he'd trot.
Horses working in a hard pace or stepping pace travel in the most hollow (concave) frame. Those in a rack or corto/largo are slightly less hollow. Those that work in a running walk lose most of the hollow in their backs and travel in a neutral frame, neither hollow nor rounded. Horses that fox trot work in the least hollow position of any of the easy gaits, just a bit more rounded than those in the running walk. All these positions are influenced by bone structure.