How do I develop my horse's topline for English pleasure competition?

A well-developed topline is one of the most visible indicators of a correctly trained English pleasure horse, and it is also one of the most honest — the muscles along the horse's neck, back, loin, and hindquarters develop only through correct, consistent work that asks the horse to use those muscles properly over time. A horse with a developed, strong topline carries itself with natural elevation, swings through its back with each stride, and maintains its frame with far less rider effort than one whose topline is underdeveloped or atrophied. The topline develops when the horse consistently works in a correct, through manner — with the hind legs engaged and driving energy forward, the back free to swing and carry the rider, and the neck and poll soft and reaching into a steady, following contact. A horse worked in this way over many months develops the muscles that make correct movement easier and more natural, which is the opposite of a horse worked in a hollow, behind-the-leg, or resistant manner whose topline weakens rather than develops. Hill work is one of the most effective topline development tools available. Trotting up moderate grades requires the horse to engage its hindquarters and lift through its back in ways that flat arena work does not, and the demand of trotting down controlled grades builds the strength through the loin and croup that supports collection. A horse conditioned on hills develops a topline noticeably different from one worked exclusively on flat ground. Transitions — frequent, well-ridden transitions between and within gaits — are the arena equivalent of hill work for topline development. Every transition that asks the horse to engage its hindquarters more deeply, reorganize its balance, and adjust its frame develops the carrying muscles of the back and loin that produce a correct topline and a correct way of going simultaneously.