Rein of Support.—The right rein, for example, is called the right rein of support when the right hand moves from right to left and the right rein hence bears against the neck. It has different effects according to the point towards which its action is directed. For example, if the hand is moved towards the front of or over the left shoulder, the effect is to bring the weight of the forehand towards that shoulder; or if the direction of the right rein of support passes in rear of the withers, the effect is felt by the increased weight on the left haunch; or if the action of the rein in this direction is sufficiently strong, it can either lead to the displacement of the haunches towards the left by setting the left shoulder, or displace simultaneously the shoulders and the haunches towards the left by pushing the horse entirely to that side.
The effect of the rein of support is extremely powerful in preventing the horse from slipping out on its side, or in restraining the horse from turning in the opposite direction.
Rein of Opposition.—If the rider opens the right rein slightly and pulls either in the direction of the right haunch or the direction of the left haunch, the rein is called the right rein of opposition. He is then said to set the shoulders in opposition to the haunches. (Notes d’Equitation.)
General Rule.—A general rule is, that at all times contact is kept with the mouth by the reins through the medium of the bit. The reins never flop. There are two exceptions to this rule allowable: during complete abandon, as at the walk; and momentarily, during flexions, as will be shown later.
The Seat.—The seat is an aid when it changes the support of the body from one buttock to the other to assist the horse in lateral movements. This movement helps to carry the center of gravity of the horse to the side toward which the movement is desired. Similarly an increase in the weight placed on one stirrup is an aid.
The upper part of the body by leaning forward or back likewise assists the horse in moving the center of gravity forward and back.