Altho Icelandic Horses have varying conformation, and can have a wide variety of gaits (or not), including fox trot,
running walk, stepping pace, the rack (tolt in Icelandic language) is a gait that some of them can do. Some can do it at
liberty, some can not. Some only do it when held up by the rider, some offer it freely when ridden.
The tolt is the same gait as the rack. Sometimes the tolt is mistakenly claimed to be a runningwalk, but that is a different gait. The following pictures show the sequence of support phases of the tolt (rack), which are as follows:
Right Hind (one foot support)
Right Hind, and Right Front (two foot, lateral support)
Right Front (one foot support)
Right Front, and Left Hind (two foot, diagonal support)
Left Hind (one foot support)
Left Hind, Left Front (two foot, lateral support)
Left Front (one foot support)
Left Front, Right Hind (two foot, diagonal support)
We'll look at one full stride, starting from the horse's weight on the right hind foot only.
Right hind only
The horse's whole body is supported by one foot only.
The next foot down, the right front, will help to support the weight in the second phase of the stride.
In this picture, the right front is not weight-bearing,
it is just starting to hit the ground with the heel (not a good thing, but the only picture I could find at the moment).
Right hind, right front
This is lateral support (both feet on the same side supporting the weight).
Right front only
The horse shifts his weight to the front foot only, and unweights the hind foot, so that the transverse hind can come in and take it's place in weight support.
Right front, left hind
The horse is in diagonal support with left hind, right front.
Left hind only
Back to a sole hind foot support.
Left hind, left front
Left front only
Again, a front foot only support.
You can see why the gait of tolt / rack is very stressful to a horse.
Left front, right hind
Diagonal support. From here, the footfall will start over again for the next stride.