We often describe define movement of a horse by the footfalls. For example, a walk is 4 beats. That is, the first foot to move is a hind foot followed by a forefoot. Then the other hind foot and lastly the other forefoot. That’s a walk.

The trot is a 3 beat movement where the left fore and right hind move simultaneously and that is followed by the right fore and left hind moving simultaneously. The canter is a 3-beat movement (for a left lead canter right hind, right fore, and left hind together, left fore, then a moment of suspension). The gallop is a 4 beat movement (left fore, right fore, left hind, right hind, and moment of suspension).

Those are the basic leg movements for a walk, trot, canter, and gallop.

But what about a rein back? The backup is considered correct when it is a 2-beat movement. It’s like a trot going backward. Why?

A horse can rein back using a 3-beat leg movement and/or a 4-beat leg movement, but we only consider it correct when it is using the diagonal feet in a 2-beat movement. I will add that I notice many trainers describe a rein back as still 2 beats when the diagonal feet are not moving at approximately the same time. This is wrong. The front and hind feet MUST hit the ground at precisely the same time, not a moment apart. If they do not land at the same time it is not 2 beats and it indicates the horse is not thinking backward and there is a mental and physical brace.

In my experience when a horse is thinking of moving back it inevitably moves back using a 2-beat footfall. When a horse is not thinking to move backward the resultant brace, resistance and lack of freedman/softness leads to a 3 or 4-beat backup.

So my question is, if a horse walks forward with 4 beats why does he walk backwards with 2 beats and not 3 beats? I assume there is something in the biomechanics that explains the disparagement but a quick search of the net has not revealed an answer to me. 

What is different about walking forward and walking backward that creates the difference in movement? I want to know. Does anyone know?