Gymnastic Groundwork is the third training element of Horsefulness Training and consists of work in hand and lunging. The goal is to help the horse move without being overloaded and moving in balance, also with a rider on his back.
Every horse has a side with long and supple muscles and a side with short, but stiff muscles. Because of this the horse bends easier to one side than the other. So a horse is either right-bended or left-bended. The horse is also not using his hind legs in a symmetrical way. The consequence of that is that the horse's point of gravity is not in the middle, but shifted to one of the front legs. So the horse moves unbalanced and not symmetrically. This is called natural crookedness.
This is no problem for the horse himself, it even gives him an advantage and you could even say that this "natural crookedness" is at the same time his "natural balance". However, if you want to ride the horse or do other unnatural activities (like lunging, or driving) then the horse has to learn to use his body symmetrically. If this doesn´t happen, this can cause al kinds of symptoms and have harmful consequences for the horse.
This young horse on the lunge is not bending on the circle. He is falling on his inside shoulder and is unable to relax the back and stretch his topline.
He can not swing his hind legs forward under his body, towards his point of gravity.
However, this is necessary for the horse to carry his rider in a proper and unharmful way.
There's really only one solution for this: doing specific and logical gymnastic exercises, first on the Ground = Gymnastic Groundwork.
Gymnastic Groundwork exists of suppling, balancing, strenghtening and straightening exercises without a rider on the horse's back.
The benefit of this is, that the horse first learns to supple and strenghten his muscles and straighten his body without adding the weight of the rider. Afterwards th rider does the same exercises under saddle.
With these gymnastic exercises the horse will learn to bend equally to both sides, relaxing his neck and head in a forward-down position. The abdominal muscles will then thighten while the back muscles will relax. This makes it possible to swing the inside hindleg forward, under the body of the horse towards the point of gravity.
When a horse is further up in the education the horse will learn to carry more weight with the hindlegs and to collect.