NOT SO MERRY GO ROUND When a horse walks, trots or canters in a square or rectangular arena, every time he really goes through the corners, he lifts his shoulders and comes out of the corner more straight and uphill. Therefore the corners are a big part of the Gymnasium anciently known sequence of exercises that empowers the horse) for a horse who takes a corner produces a small Shoulder In. Shoulder in, is in fact a horse walking as if going through a corner, but then keeps his shape and walks in a straight line forward.
Of course, when you work a horse free in a rectangular space which is to large, the horse will often cut the corners. That is why a picadero was invented. It is a square measuring 12 by 12 or 15 by 15 meters. Within the picadero, just following the track in walk, trot or canter will benefit your horse by lifting his shoulders each corner.