So, a long, long time ago, in a galaxy far, far away, I said I was going to start a feature here at the Q:P about horses, called the Writer's Beginning Guide to Horses. The goal of this feature can be found in detail with the first entry here, along with my background, but in a nutshell, I wanted to compile a resource for writers who want to put horses into their novels. A simple, easily-categorized resource to answer common misconceptions and questions.
So finally, eight months later, I am writing the second installment. Today's installment is about the gaits of horses, or, the different "gears" they have, if you will.
The most common breeds of horses have four major gaits. There are horses that have more than four gaits, but they are admittedly one place where my knowledge is lacking. You can read more about these horses, called gaited horses, here.
The first gait is the walk. This is the standard gait, and is the easiest to understand-- it's a walk. It's quite obviously the slowest of the gaits, and is what's called a four-beat gait, meaning that each of the hooves hit the ground independently of each other. The horse has three feet on the ground at a time during the walk. As far as a rider is concerned, the walk is the easiest gait to ride.
The next gait up is the trot. The trot is a two-beat gait, meaning that the feet move in pairs, with two feet on the ground and two feet in the air at the same time. The pairs of feet are on diagonals, meaning that the front right and rear left will be off the ground at the same time, and so forth.
For the beginning rider, the trot is usually the hardest to ride physically. An experienced rider can sit the trot, meaning they match the motion of their hips to the motion of the horse and do not bounce up and down in the saddle. Alternatively, in English disciplines (and more and more common everywhere regardless of discipline), the rider can post, which means to rise up and down in the saddle with the rhythm of the horse, taking most of the jarring out of the trot.
The next gaits are technically the same gait, only at increased speed and with a difference in beat count. The first stage over the trot is called the canter (in English disciplines) or the lope (in Western). The canter or lope is a three-beat gait, which is rather much harder to explain in this brief overview, and therefore I will re-direct you to this resource which explains it in detail if you care to research further. If your characters are just on a romp through the countryside, chances are they are moving at a walk, trot, or canter/ lope.
The faster version of the canter/ lope, and fourth gait, is the gallop. The gallop is the fastest gait, and you've seen it before if you've ever seen a horse race. It is a four-beat gait, like the trot, but the pattern of footfall is different and there is a moment of suspension where all four feet are off the ground at the same time. If your characters are running away from someone on horseback, chances are they are galloping.
Some special concerns with the gallop though: most horses can't keep this gait up for more than a few miles. For novels set in periods where horses were working animals, this might be increased slightly because they would naturally be in better shape. For a horse living a cushy modern life, however, it's probably only a mile or two.
For the rider: the canter is probably, aside from the walk, the easiest gait to ride. The horse's back takes on a swaying, rocking-horse motion that is spaced out much more than the trot and allows the rider to sit it much more easily. The gallop is similarly easy for an experienced rider, however, for a beginner it's probably the most difficult psychologically due to the speed-- up to 35/40 mph depending on the breed and physical condition of the horse. A rider may also have to hollow their back, or lean forward and sit up out of the saddle to ride the gallop rather than being seated normally.
There you have it! Any questions?