I would work on transitions (walk, trot, halt, trot, walk, etc) on a circle before cantering- the you and the horse look kind of tense together and she is very tense through her neck and jaw. That will transmit through her back and body and makes for an unpleasant ride. If you could work on a smallish circle using a direct rein to bend her (thereby not pulling back) and relaxing through your whole body (use some centered riding stuff- not holding your breathe, breathing from the diaphragm, softening your eyes and loosening your body to be light and flexible in the tack) you could start to get the mare to relax herself. That may solve some of the issues you say you're having and that others have picked up on.

I have the same exact problem- I lock up through all of my joints and end up being stiff, which in turn makes my mare brace against me. If I concentrate on not concentrating so hard (haha) it gets much better.


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