My trainer rides 3 - 6 horses a day plus does the regular barn chores. Now if I could ride and work as much as she does I would probably be as fit as her. But riding that often is unrealistic for most people. Rider's skills and abilities depend on general endurance. The longer you ride without tiring the more oxygen you need to take in.
Basic conditioning trains the rider's body as extensively as possible .
Eventing, jumping and dressage have special aids that are to be applied over long periods of time without tiring. They are given to the horse quickly, and they must be firm and continuous . You need to be agile , in order to move with the horse, speed and strength endurance are needed to apply the aids with your legs, back, seat, stomach and arms. You must be able to coordinate your legs, back, seat, stomach and arms to give the aids quickly and quietly. Please be careful when doing any exercise, don't overdo it.