Sit the Trot
REALLY! If you want your schooling session to be a good workout, sitting will make you that much more active and effective with your aids. And please don't tell me that you can't sit. To me, that just means that you won't practice or you tried and it was uncomfortable or difficult. Well, if man can fly to the moon, you can sit the trot! It's just a question of wanting to do it enough and accepting that there's no quick fix--you just have to try and try until it finally happens.
But you can make it doable. Tell yourself, "I will do the best I can do," instead of, "This is so hard that I can't do it." Read your body and capabilities and don't expect to immediately sit for 45 minutes. Mix a few strides of sitting and a few of posting, gradually increasing the sitting until you're just doing it! If you've struggled with sitting, you're probably trying to hang on by pinching your knees and gripping with your thighs. But that just lifts you out of the saddle and away from your horse. And the farther you lift out of the saddle and feel uncomfortable and insecure, the more you grip and the worse it gets, until you're thumping on your horse's back. Prevent this by focusing on sitting down on your seat bones, taking the "bounce" in your abdominal muscles and relaxing your thigh and opening your knee so that gravity pulls your leg down.
Mix It Up
A good workout isn't all about one gait or one exercise. It's important to walk your horse on a long rein for at least 15 minutes before you start working. Let him go long and loose and relaxed like a pendulum. Better yet, get out of the ring if you have a chance. GO! Don't take him straight from the barn and start schooling. Begin with a little hack so he can breathe and stretch first. In the long run, you and he will have a better workout. And remember to cross-train. Go out in the woods and trot. Take a trail ride. Go up to the jumping arena and trot ground poles or do a big posting trot and let your horse go more forward. Variety is essential to prevent boredom and keep your horse from getting ring sour. But it also exposes both of you to new experiences. Then, when you go away to a strange facility for a show, you'll still be confident instead of scared. And he'll be relaxed instead of tense.
To learn how to nail perfect figures for higher dressage scores, see Mette's article "Perfect Figures = A Key to Dressage Success" in the April 2008 issue of Practical Horseman magazine.