The thighs should fall as vertically as possible. The calves are in contact without gripping.
A rider must also make sure his joints are working correctly. Like a skier on a hill with many humps, he cushions the movements allowing his hip, knee and ankle joints to give. The same applies at the rising trot. Stay well over your feet to ensure you don’t hang on to the reins.
Leg pressure must, under no circumstance, be continuous. The grand theory of the older instructors who believed that to be a good rider it was compulsory to have strong legs: «legs, always use your legs» seems to me an obstacle in establishing effective communication with the horse.
I believe that the best leg action is the one obtaining the maximum effect, using the minimum pressure.