(7) ...from propulsion to impulsion...
(7)...c. ...turns tend to disturb the horse's movement as long as propulsion, coming from the hindquarters, because of their slant, does not line up with the forehand...
Yes, the hind legs in most green horses do not alike step towards the center of its weight... Consequently the support of the body is flawed, which makes it difficult for the horse to turn correctly both sides alike... Hence Steinbrecht's advice...
(7)...d. ...for this reason the rider with well developed feeling will make sure he calls the horse's hind legs to support the forehand and to propel it on...
What does this mean in plain text...? The horse is too fast. It does not know how to turn. Most likely it will be difficult to sit... It may or may not have come to the rider's hand... It may or may not be able to support itself... No wonder he is quick to confirm that only riders of talent and experience will be able to master these five aspects simultaneously...
(7)...e. ...such riders with a fine feel will see to it that, according to the turning diameter chosen, they lead the horse with prepatory arrets into the collection requires while introducing an appropriate degree of lateral bending... and thus prevent any confusions of either gait and/or posture...
Oh boy, what a beautiful statement...! And an illustration of the problem that underlies all of Steinbrecht's Gymnasium. The talented and experienced rider will understand his advice in an instant. The novice and the well meaning amateur remains uninstructed...
There is one additional aspect to this, however, which should not remain unmentioned... Steinbrecht here clearly advises the moderation of propulsion by the means of impulsion. I.e. not gaining ground but the transformation of energy from horizontal to vertical makes for a trained and agreeable mount...
The question remains, at which age is the horse able to collect...? Only after the sacrum, which is the pivot of posture and a fulcrum of the horse's movement is fully ossified...? At age seven...?
Well, ...obviously in those year before the horse turns seven the rider must have means to moderate the horse's tempo... What are his options...? And, which posture is the best in this phase of the horse's life...?
We'll see how Steinbrecht addresses and answers these questions... And what modern finding will have to add...