How do you fix a horse that rushes in medium trot in dressage?

A horse that rushes in medium trot — speeding up, falling onto the forehand, losing rhythm, or running through the transition into medium rather than showing a controlled lengthening with maintained rhythm and balance — is typically showing either insufficient collection in the working trot that preceded the medium, or insufficient responsiveness to the half-halt that should prepare and contain the transition. The most effective correction addresses the preparation rather than trying to manage the medium trot itself once it has started: if the preparation is correct, the medium trot will be correct; if the preparation is inadequate, managing the medium trot after it has begun is always less effective than improving the preparation. The preparation for medium trot should include one or more clear half-halts that shift the horse's weight slightly toward the hindquarters and reorganize its balance before the lengthening is asked — a horse that is genuinely balanced and carrying before the medium is asked will lengthen from that balance rather than falling forward. Testing the quality of the preparation by giving the medium trot aid and observing whether the horse lengthens both forward and upward with maintained rhythm, or drops onto the forehand and quickens the steps rather than lengthening them, reveals immediately whether the preparation was adequate. The transition back from medium to working trot is as important as the transition into medium: a prompt, balanced transition back that shows the horse shortening its stride while maintaining rhythm and balance confirms that the medium was genuinely from collection rather than from running. Practicing many short medium trot sequences — two to three strides of lengthening, then back to collected work, then lengthening again — rather than long sustained medium trot develops the horse's ability to extend from collection rather than by falling forward into speed.