How do you develop impulsion in a lazy horse?

Developing impulsion in a lazy or sluggish horse requires establishing a prompt, genuine response to the leg aid before any quality of impulsion can be developed, because a horse that does not respond reliably to the leg cannot produce the elastic, forward energy that impulsion represents regardless of how strongly the rider drives. The first training priority is installing a quick, honest response to the lightest leg aid: applying a light leg aid, waiting briefly for the horse to respond, and if no response comes escalating immediately to a stronger aid — perhaps a tap with the whip behind the leg — followed by an immediate return to the light leg the moment the horse moves forward. The escalation must be definitive enough to produce a genuine response, and the return to the light leg must be immediate, so the horse learns that light leg means go now rather than that the persistent strong leg is the actual signal. Clinton Anderson's sensitization approach — light aid first, escalating only if needed, immediate release — applies directly to this problem. Once the horse is responding promptly to the leg, the transition work that actually develops impulsion can begin: sharp transitions from trot to canter, from walk to trot, and within gaits from a more forward to a shorter but more active gait develop the hindquarter engagement that impulsion requires. Cavalletti and poles on the ground encourage the horse to lift its legs more actively and can increase the horse's natural desire to move forward with more energy. The rider must avoid the common mistake of applying a constant strong leg, which teaches the horse to become even duller by providing consistent pressure that it learns to ignore; instead, using the leg definitively when needed and removing it completely when the horse responds trains the horse that the leg is a meaningful signal rather than background noise.