Proper position has little to no impact on the rider OR the horse; conversely improper position has a huge impact on both the rider AND the horse. Ankle, knee, and hip joints / angles are key to functional and comfortable riding for both members of the team. Errors in any one of these cause exponential errors in performance of the horse and rider team. So it’s important to get it right. Here’s some good tips from Wendy Murdoch, a link to her book, and a quick video sample.
For the tips and the article in MyHorse Daily, click Cantering on a balance ball!