Question: I read the post about the Icelandic having a "hitch" in his
 tolt. Well my STB also is having a hitch in his rack on his right hind
 leg.  He was gaiting fine, until late November, then one of the girls at
 the barn said he looks sore.  He has been seen by a very respectible
 equine vet and he said he is not lame, but "ill-gaited."  My horse walks
 fine, trots fine, canters fine, but at the rack he looks off.  He does
 do this all the time, but not consistently if that makes sense.  He
 takes a few correct steps and then a few incorrect steps, so it's like
 he goes in and out of it.  VIXL sounds just like what he does, can you
 explain it further please?

 Hello.

Vixl is when a horse mixes gaits in such a way that the horse tolts/racks, but
because of tension it does a mix and it feels like it is jumping an inch in in
loose air for a split second an then it tolts/racks again.  The footfall there
is very complicated and I'll spare you an exact explanation, as vixl is rather
rare.
But a quick explanation is that the horse is tolting/racking, then it wants to
go into trot, and takes half a step of trot.  But because the horse does the
transition incorrectly, for a split second it would have to put one of the hind
legs down on the ground on the same spot as one of the front legs is standing.
As it can not manage to remove the front leg in time, the horse decides to keep
the hind leg in loose air untill it has rearranged where all the legs are and
can step down with the hind leg.  It all happens very fast, and with some
horses you feel that everything is going crazy under you for a split second.
It is extremely uncomfortable to sit vixl.

Training vixl out of a horse demands a very careful rider.  The reason for the
vixl is that the horse is tense, and it does not manage to keep the gait
because the whole topline is tense, at least for the split second.  So tension
must be avoided, and crude aids.  Reins must be used extremely carefully
(holding them steady, not giving any unnessary clues).  The horse can regain
balance by riding it carefully like this for a long time (maybe weeks) in a
careful way, and do exersises to loose the tension.  Very much care must be
taken when going slow or fast, as that is difficult for a pacy horse, and that
is the time when the horse that does víxl is most likely to do so.  Do not
loose courage, this is not an easy fault to correct.
So, a horse that does vixl often can just manage the rack/tolt at one certain
speed to begin with (work on finding the ideal speed for your horse).  When you
get the horse into the tolt/rack, relax and try not to interfere with the
horse, so that it can learn to relax a bit in the gait, of course though not so
much that it gets all on the forehand.  It's a thin line you have to walk
there, but every stretch of gait without vixl is an accomplishment.  Gradually
you can ask the horse to do a bit slower and a bit faster tolt/rack, but try to
work on success, not failure, in the horse.
Working on releasing the tension at walk is also important, so that the walk is
not pacy and tense.  Do all the things that your horse can do to improve being
athletic at the walk, for example serpentines, sidestepping, turning on the
forehand and such things.  Allow the horse to drop the neck once in a while at
the walk and learn to enjoy the relaxation.
It is also good that he trots easily, as he can then relax at the trot.  So,
mix walk and trot training with short episodes of tolt/rack to begin with, and
gradually make the episodes longer, as the horse starts to manage it.
Pacyness and vixl often goes hand in hand, and maybe your horse connects the
lateral gait with a racing experience he has had before.  Maybe your horse is
also very pacy in the rack as he's thinking about the fast pace, if he was a
pace racer.
Happy trails.
Lukka.