"in order for true partnership to develop between horse and rider, there has to be balance. the rider's centre of gravity and the horse's centre of graity have to be aligned. this makes for economy of movement and only the lightest aids to direct our horse. the more balanced we are, the more secure we are.
p.s.
the rider's body must constantly regain any loss of balance
the harmonious picture of hrose and rider acting as one is presented only when the rider is balanced. this is of course, what all equestrians of all disciplines constantly strive for.
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manual p 69 how to improve position