Trot (horse gait)
From the standpoint of the balance of the horse, the trot is a very stable gait, and the horse need not make major balancing motions with its head and neck. This is a common gait that the horse is worked in for dressage, due to its many variations.
The speed of a regular working trot is averages 8 to 12 km/h (5 to 10 mph), up to 19 km/h (12 mph) in a horse driving trials marathon. Harness racing horses are considerably faster. Other variations, such as the "jog trot" used in western pleasure competition, may be much slower.
Eadweard Muybridge was the first to prove, by photography, in 1872, that there is a "moment of suspension" or "unsupported transit" during the trot gait.
Types of trot
The trot can generally be classified as "working", "collected", or "extended", depending on the amount of engagement and collection of the horse. By the rhythm, one may distinguish a true, two-beat square trot, when each diagonal pair of hoofs hits the ground at the same moment, from a four-beat intermediate ambling gait, such as the fox trot or the "trocha" sometimes seen in the Paso Fino.
Different speeds and types of trot are described with the following terms (from slowest to fastest):
- Jog trot: seen in western horses, it is a slow, relaxed trot lacking the suspension of a working trot, with shorter strides. It is easy to ride because there is less "bounce." The head of the horse is carried low, and while the hindquarters are engaged and underneath the horse, there is less impulsion than in a dressage-style collected trot.  
- Collected trot: a very engaged trot where most of the horse's weight is carried toward the hindquarters. The frame is compressed, the stride length is shorter than any of the other trots, with the horse taking higher steps. The horse is lighter and more mobile in the collected trot. 
- Slow trot (harness) or Road gait (roadster): slower than a working trot, but faster than a jog trot, this gait is one of the gaits used in [harness classes at horse shows.
- Working trot or Trot: the natural trot of the horse when under saddle. The stride length is "normal" for the horse (note: some breeds have naturally shorter or longer strides). It is a gait between the collected trot and medium trot.  
- Medium trot: a trot that is more engaged and rounder than the working trot, with moderately extended strides. It lies between the working and the extended trot. The horse has good, solid impulsion.   
- Park trot: Sometimes simply called a Trot in a given class, seen in saddle seat and fine harness classes for Saddlebreds, Arabians and Morgans. It is a showy, flashy trot with extreme elevation of the knees (forearm is horizontal or higher and the hind legs are extremely flexed). The head is held high, and while at times a horse may hollow its back and lose cadence in an attempt to achieve high action in front, the hindquarters must be engaged for it to be properly performed.   
- Lengthened trot: a trot with lengthened strides. It differs from the more advanced extended trot in that is does not require the horse to bring its weight as far back on its hindquarters.  
- Road trot or Show at Speed: seen in roadster classes, this gait is similar to a racing trot, but much slower (suitable for an arena setting) the head is still collected. While the stride is still at maximum length, the step is still high and animated.
- Extended trot: an engaged trot with long strides, where the horse stretches its frame, lengthening the strides to the greatest degree possible. The horse has a great amount of suspension. The back is round and the horse's head just in front of the vertical. , .
- Racing trot: seen in harness racing horses that race at the trot, such as Standardbred. The stride is at its maximum length, with a great deal of suspension. The hind leg in a diagonal pair may begin to ground before the front. Unlike the extended trot, the neck is not round but extended out.   
Haute Ecole variations on the trot
In advanced dressage, two additional forms of the trot are used:
- Passage: a slow, elevated, extremely engaged and collected trot. The horse moves like it is in slow motion, with a long moment of suspension between steps. A very advanced movement.   
- Piaffe: an extremely collected trot in place, where the horse carries most of its weight on its hindquarters and does not move forward except for a few inches per stride at most.   
Riding the trot
There are three ways the trot may be ridden:
- Sitting: The rider's seat remains in the saddle the whole time, following the motion of the horse, without bouncing. This is preferred for show ring western riding and in dressage, especially at the upper levels. Sitting the trot gives the rider optimum control because he or she can use the seat and weight to influence the horse, asking for upward or downward transitions, turns, and to decrease or increase impulsion. It is also a test of equitation, proving that the rider can quietly move with the horse. The jog, which is the preferred gait of western horses, is generally smoother and less-bouncy than the working and extended trot of the English-style horse. Sitting can be very tiring for the rider, especially if performed by riders who have not built up their stomach and back muscles, or if riders are on an extremely powerful mount with a big trot. To sit the trot, there is a slight forward and back movement of the lower back and stomach as the rider's hips follow both the up and down and side-to-side motion of the horse. To absorb the impact of the trot, the rider relaxes through the hips, the stomach and lower back, as well as the legs. The rider's upper body remains upright and quiet. The rider's hands remain steady. The lower legs remain relaxed and only come into play when the rider gives a leg aid. If a rider cannot sit the trot and is bounced around, the rising trot is preferable, as not only is the rider uncomfortable, the constant slamming of the rider onto the horse is uncomfortable for the horse, who will hollow its back and stiffen its movement.
- Rising or Posting: The rider makes an up and down movement each stride, rising out of the saddle for one beat, and lowers (sits) for the second beat. When the rising trot is performed correctly, it is comfortable for the rider and easy on the horse. This is preferred for show jumping, hunt seat, eventing (the jumping phases), saddle seat, lower-level dressage, and most other English-type riding as well as endurance riding. Although this does not provide as much control as sitting, it frees the horse's back. In the rising trot, the rider allows the horse's movement to throw his or her seat a bit out of the saddle. When coming back down, the seat touches down lightly rather than slamming down on the horse's back. Except in Saddle seat riding, rider's shoulders maintain a slight forward incline throughout the rising trot, instead of the upright, vertical position seen in sitting trot. The shoulders and lower legs remain in relatively the same position when the rider is both rising and sitting and the hands also stay in the same position as the rider rises and sits.
- Half-seat or Two-point: Variations are also called jumping position, Half-seat involves the rider getting the seat bones off the saddle and keeping soft contact with the pelvis, two-point involves the rider raising the seat and pelvic bones. In both cases, the rider remains off the saddle and does not sit. This provides a great deal of freedom for the horse's back. It also offers the least amount of control for the rider. These positions are rarely used at the trot, although both are common at the canter for jumping riders. Two-point also requires a good amount of strength in the rider's legs, which must be developed slowly.
A rider posts to one side or the other at the trot, called a "diagonal." Diagonals are used in the rising trot help to keep the horse balanced, and are also useful for timing certain riding aids, such as those for the canter. When the rider is on the correct diagonal, the rider sits as the horse's inside hind leg and outside foreleg are on the ground, and rises as the outside hind leg and inside foreleg are on the ground. A rider can learn to recognize diagonals by feel. However, less-experienced riders discreetly check for the correct diagonal by a quick glance down, using peripheral vision.