From the maufactor''s website:
"The Dynamic 3 is a good choice for horses with a straighter back, short back, ponies, young horses, wide barrel horses, baroque horses, Friesian horses. Because the Dynamic 3 keeps the rider off from the horse’s lower back, this model is exceptionally useful when developing the topline of, for example, the young horses or older horses with weak lower backs, or those returning to work after long layoffs. The square cantle gives more openness in the seat allowing the rider an independent seat"