If you and your horse can't move freely, it becomes difficult to ride him well.
Before- Here a dressage rider in Girona, Spain is asking his horse to come through in his habitual way while bracing his body. He commented, "this horse is lazy."
When your body moves freely, your horse can move freely too.
After- Change of body use. Here the dressage rider has released his bracing posture and later commented, "I have never felt my horse this free ever, and he doesn't feel lazy."