Longeing is more than a horse running around on a circle. Longeing is mainly used to prepare a youngster to become a riding horse or to rehabilitate a so called “problem horse”, but it is also a very
valuable and diversified trainings component for more advanced and older horses.
Through physiological and well thought through longeing the horse gains more fitness, builds up muscles and finds his balance in all gaits. The horse learns to stretch his topline and to activate his underline, whereby the back is able to move in its three-dimensional swinging. The horse has to take more responsibility on his own balance, because he has to move more on its own feet with less guidance from the trainer.
However the trainer is still able to observe and correct, where necessary, the movement and the shape of the horse in all gaits and guide him from more distance.
The structural theme in longeing is the LFS (step 1, 2 and 3 of straightness training):
*Lateral bending * Forward-down tendency * Stepping under 
The horse is asked to walk with correct lateral bending on both reins, which makes him release his back muscles and with this stretches the head and neck forward downwards. Also, it brings the inside hip forward so that the inside hind leg can step under the point of weight.
With a nice LFS the horse moves in balance and in a correct and supple self-carriage.
The following exercises can be developed on the longe line: LFS on a bigger circle, walk, trot, canter, transitions within a gait and from gait to gait, halt, s-change and on a more advanced level, if the horse is physically and mentally well prepared, you also can start to work on collection on the longe line.
In Straightness Training we always lunge with a cavesson. We never lunge with the lunge line at the bit, because thereby we can’t ask the horse anymore to give us a correct stelling and he also could tilt his head.
Impressions ST Longeing Grade III with Whoopy