To maintain a straight seat you must tighten your own lower back. If you regain your balance backwards too early this will work against the horse s transition. Lean backwards and regain the equilibrium after the horse has begun the transition. When the horse has transited, say thank you by slacking the reins. . One leg - one start.
Enforcement is made by use of the whip.
Just use your leg when you want the horse to change gaits or increase tempo. Soft sensitive leg - just the lower leg. Hard unsensitive leg - all of the body. To maintain the upright position you must tighten the abdominal muscles. If you regain your balance backwards too early this will work against the horse s increase of speed.