What role does long and low work play in developing suppleness in dressage?

Long and low work — riding the horse in a stretched, forward-and-downward frame with the neck extended and the horse reaching to seek the contact at a lower position than normal — is one of the most valuable exercises in dressage training for developing longitudinal suppleness, rewarding the horse's relaxation, and checking the quality of the throughness that normal training is developing. When ridden correctly, long and low work requires the horse to release the muscles of its neck, back, and topline in a genuine stretch — reaching forward and down to find the contact rather than simply dropping its head because the rein is given — and this release is both physically therapeutic for muscles that have been working in collection and psychologically rewarding for the horse that has been doing focused gymnastic work. The quality of the long and low tells the trainer a great deal about the quality of the work that preceded it: a horse that stretches genuinely forward and down into the contact, maintaining rhythm and impulsion as the frame lengthens, is showing that it was genuinely through before the stretch was offered; a horse that simply drops its head without seeking the contact, or that loses rhythm and energy in the stretch, is showing that the previous work had some restriction or blockage that the stretch reveals. Long and low work is used productively at the beginning of training sessions to warm up the muscles and establish genuine forward movement before demanding collection; within training sessions as a reward and check after periods of more demanding work; and at the end of sessions to allow the muscles to cool down in a relaxed, extended frame. Classical trainers including the German training tradition consistently emphasize that a horse that cannot stretch genuinely forward and down when given the opportunity has not been working correctly, making long and low the standard test of whether the training session's suppleness work has been genuinely productive.