BILL— Among beginnerish riders it’s probably because it’s the instinctive way that they think they should turn their horse. Fairly early on riders get past that stage, yet the problem persists. This is usually because they underuse their supporting outside aids. We have all heard many, many times “inside leg to outside hand,” but this mantra neglects the importance of the outside leg which keeps the horse from bulging out.
The other factor is many riders’ over optimism about just how much their horse actually bends. As an experiment go out in a sand arena with a lunge line and trace part of the arc of the 20 meter circle. Then mark off a six-foot length of that circumference which is about how long your horse is. Look at half of that length—the equivalent of your horse’s neck. Not much bend there, is there? Sometimes the overbending occurs because riders incorrectly assume the rest of the horse is bending as much as the part in front of them!