In class, doing ronde de jambe a terre, there is a tiny section of movement where you can feel the rotator muscles, the back of the thigh, in a struggle to hold your turnout in both legs.
It is the pointe where you leave a la seconde and move toward a la arriere.
A lot of muscle strength is needed right here. As the foot draws away from a la seconde, pulling the leg seemingly away from the hip socket in a lengthening pull, the core muscles pull up and away from the legs, and the supporting leg pushes down into the floor to also keep its length.
You try to keep the turnout as the leg is circled toward a la arriere. You keep the spine long as the working hip opens, but only as much as it needs to, to reach the arriere position. I prefer an arriere position where the working leg is behind the working hip, not crossed over to be behind the spine.
Crossing over to the center point of the body brings too much compensation as very few people have the turnout to even attempt this. There is enough strength required simply to maintain turnout and body position without this extra challenge.
Hopefully, even in advanced classes, the teacher does some ronde de jambe a terre very slowly during the exercise, to allow activation of the rotator muscles and maintenance of the full body position.
If this does not occur in class, you definitely need to practise this at home or after class.
The mental image is full of finer details – doing this in your imagination will actually help when you stand up or do the floor exercise.
First, review the muscle dynamics:
*** The working foot draws away from a la seconde aiming for the widest circular movement possible;
*** The supporting side core muscles pull up and away from the pull of the working leg, with a push down feeling through the supporting leg, all of which maintains the elongation of the whole body posture;
*** This work in the supporting side also keeps the body weight from being pulled back onto the heel;
*** This elongation is therefore maintained when the working hip opens, allowing the optimum result in the turnout as the a la arriere position is reached;
*** Once the position is reached, the torso above the waist is still square and the working hip is not bunched up toward the body, but the whole working side is elongated;
*** You can let go of the barre, lift the foot up an inch and maintain your position.
As a floor exercise, lie down on your back, use a rolled towel under the neck to help keep it supported and relaxed. You can relax the arms across your stomach. Do a tendu to your a la seconde position. Then circle back one inch, without losing your body position or supporting leg turnout. Move the leg back to your a la seconde position. Repeat ten times each side. Draw out and down with the foot, elongating the leg.
Turnout is harder to hold in pointe shoes, so your pre-pointe work is crucial.
Always relax and stretch after practising, and often during class. Turn IN between exercises. Building up tension is not the same as strength, and will diminish your muscle tone.
Have a day of rest. If you feel driven to work your daily routines every day, do it for the finer details mentally on one day. This not only develops concentration, but since optimum results depend so much on concentration, you are still working, not cheating.
The studies in neurobiology indicate that your brain thinks you are "really" doing it. But that's another loaded topic.