This rule was fazed out years ago, as it was considered that yhe horses carrying the dead weight of the lead were at a significant disadvanatge to those carrying just a rider above the required weight. (a rider can shift their weight when needed, the lead plates obviously could not) So it was ruled that a minimum weight requirement was not necessary to give a level playing field in the sport. Personally, I am alway amazed when I hear of people riding their horses 5-6 days a week. What about lunging? A horse is ultimately not made to carry any weight on it's back, and regardless of rider being over or under-weight this puts enormous stress on the horse's body, then we add in schooling, jumping and travelling at speed? Why not ride 3 days and lunge the rest and give your horse a break while maintaining the fitness and education?