Trot
The trot is a two-beat gait that has a wide variation in possible speeds, but averages about 8 miles per hour (13 km/h). A very slow trot is sometimes referred to as a jog. An extremely fast trot has no special name, but in harness racing, the trot of a Standardbred is faster than the gallop of the average non-racehorse.
In this gait, the horse moves its legs in unison in diagonal pairs. From the standpoint of the balance of the horse, this is a very stable gait, and the horse need not make major balancing motions with its head and neck.
The trot is the working gait for a horse. Despite what one sees in movies, horses can only canter and gallop for short periods at a time, after which they need time to rest and recover. Horses in good condition can maintain a working trot for hours. The trot is the main way horses travel quickly from one place to the next.
Depending on the horse and its speed, a trot can be difficult for a rider to sit because the body of the horse actually drops a bit between beats and bounces up again when the next set of legs strike the ground. Each time another diagonal pair of legs hits the ground, the rider can be jolted upwards out of the saddle and meet the horse with some force on the way back down. Therefore, at most speeds above a jog, especially in English riding disciplines, most riders post to the trot, rising up and down in rhythm with the horse to avoid being jolted. Posting is easy on the horse's back, and once mastered is also easy on the rider.
To not be jostled out of the saddle and to not harm the horse by bouncing on its back, riders must learn specific skills in order to sit the trot. Most riders can easily learn to sit a slow jog trot without bouncing. A skilled rider can ride even a powerfully extended trot without bouncing, but to do so requires well-conditioned back and abdominal muscles, and to do so for long periods is tiring for even experienced riders. A fast, uncollected, racing trot, such as that of the harness racing horse, is virtually impossible to sit.
Because the trot is such a safe and efficient gait for a horse, learning to ride the trot correctly is an important component in almost all equestrian disciplines. Nonetheless, "gaited" or "ambling" horses that possess smooth 4-beat intermediate gaits that replace or supplement the trot (see "ambling gaits" below), are popular with riders who prefer for various reasons not to have to ride at a trot.
Two variations of the trot are specially trained in advanced dressage horses: the Piaffe and the Passage. The Piaffe is essentially created by asking the horse to trot in place, with very little forward motion. The Passage (rhymes with "massage") is an exaggerated slow motion trot. Both require tremendous collection, careful training and considerable physical conditioning for a horse to perform.
Read more about this topic: Horse Gait