Very good article...it brings me to think, not all "horse training" issues, may be just discomfort or pain of some sort.
I would think one should first measure the horse's performance under saddle to his/her performance in groundwork because groundwork is the fundamental. If there is a significant difference between the two, the appraise the issues in this article; if not, go back to your ground work routine. (Too many horsepeople overlook the importance of goundwork!)
Great advice. In my experience most horses in a lousy mood have some pain or discomfort. Sometimes it's as simple as stiffness that needs some walking out before real work begins or even a change in the weather making them feel a bit down but never nothing.
Thank you all very much for your feedback. Daniel, I completely agree that comparing your horse's behavior and movement without the influence of tack or rider is extremely valuable.