There are many building blocks that lead to a horse being ready to give you proper impulsion. You have to have a few basics down and well practiced first. Take a look below.
1- Rhythm: It is the result of mental and physical relaxation. When the horse is relaxed, he is able to step into the natural rhythm of the four natural gaits: walk, trot, canter, and the rein-back. The walk is a 4-beat movement, the trot 2-beat, the canter 3-beat, and the rein-back 2-beat. A horse that trots in rhythm is trotting in a clear 2-beat rhythm in a steady tempo. There is good rhythm and bad rhythm: Good rhythm is when the horse’s canter is a true 3-beat, bad or incorrect rhythm is when it becomes a lazy 4-beat. Rhythm faults in the walk are when it comes close to 2-beat, and in the trot when it resembles a lame, hopping horse.
2- Suppleness: A dressage horse is ultimately an athlete, and every athlete requires a certain degree of flexibility. Suppleness is the looseness and flexibility of the horse’s body. There are two types of suppleness: longitudinal and lateral. Longitudinal suppleness is the looseness of the horse’s haunches, back, neck, poll, and jaw, giving him the ability to swing forward while remaining fairly on the bit. Lateral suppleness is the degree to which a horse can bend his body and neck sideways, either to produce a circle or to move sideways.
3- Contact: When the horse is accepting the rider’s hands, seat, and legs, it is said that he is offering good contact. Many people mistake contact for the horse being on the bit. That is not necessarily true and denotes riding with the hands alone. A horse moving under a rider is in contact with his seat, legs, and hands. Good contact is when the horse accepts and responds to seat and leg aids while maintaining a round outline with a mouth that is relaxed and accepting the bit. You can point out good contact when the horse’s back is raised, his quarters engaged, his poll the highest point, his jaw relaxed, and his nose a hint in front of the vertical (That is also a sign of good riding and training).
4- Impulsion: Free-flowing energy initiated by the rider, causing the horse’s back to swing, his quarters to engage, and his forelegs to articulate is impulsion. Good impulsion is mirrored through a horse that appears to have an innate desire to go forward with active, lively steps. How far the horse steps underneath his barrel and how much he engages his hocks are both measures of impulsion. Basic training regulates the horse’s engine so that impulsion becomes second nature to the horse and the rider does not have to push all the time.
5- Straightness: Horses are naturally crooked, so straightening them is the job of the rider/trainer. For example, many horses canter with their quarters slightly in. Crookedness is caused by uneven lateral suppleness, I.e. One side stiffer than the other, and a weaker hind leg. Good training focuses on developing both sides and hind legs of the horse equally, which eventually leads to absolute straightness. A horse is truly straight when the hind foot steps in the line of the front foot (or sometimes a little deeper to the inside in the event of collection).
6- Collection: The pinnacle of the Training Pyramid, collection is the ultimate goal for the dressage horse. When all the previous elements are present, collection just happens! Collection involves the lowering of the croup, lightness of the forehand, and shorter and higher steps. Collection is possible in the walk, trot and canter, and is achieved by collecting exercises and refined by little half-halts. A rider on a horse doing a great collected canter feels as though he/she can let go and the horse would still maintain perfect rhythm and self-carriage without any interference from the rider.