The rider's movements at each gait and speed are going to be quite distinctive: walk, working walk, collected trot, extended trot, sitting trot, two point trot, canter at varying degrees of collection, gallop, over jumps, etc.--and that's just English. Presumably, these could be programmed like any movement.
As for "some effort," the exertion can be very large, akin to running--because the rider isn't just sitting, but constantly gripping with his or her legs, posting (moving up and down) at the trot, using other muscles for balance, and moving the trunk muscles in concert with the horse to keep the upper body and arms independent. An hour-long lesson will work up a good sweat, even in a cold arena in the winter, and novices experience days of muscle aches just like anyone who takes on any new form of vigorous exertion.