LONG REINING IS an art and it will only be of benefit if the handler is confident and competent.
Although this form of groundwork can help both young and older horses alike, I tend to long rein my youngsters the most as it teaches them to move forward independently, work into a contact and not rely on being led everywhere by a human.
I would always advise extreme caution when long reiningahorse of any age, however. Young horses especially have quick reactions which means that the handler must be in the right position at all times to avoid either getting the reins in a tangle or finding themselves too close to