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I've written considerably about the finer details of pirouettes en dehor and fouettes, and turns a la seconde. For pirouettes en dedans, the daily routines of securing a straight up and down press up or releve, with relaxed arms, head and shoulders, is the basis for turns en dedans too. The following analysis is to help you with working smarter, developing the correct muscle memory, and attaining optimum results.
If you can now do a series of 8/16/32 en dehors pirouettes from fifth position, with relaxed spotting and a straight up and down releve, then change the series to en dehors/en dedans, en dehors/en dedans, all going to one direction. It doesn't take much force.
You can also do this without any help from the arms, by putting your hands on hips or shoulders, and making sure that the turn is coming from your legs, back, and from a grounded demi plie. In other words a good push off from heels pressed into the floor.
A pirouette en dedans from a relaxed fourth position plie, requires a sharp releve, turning out the supporting leg towards which you are turning, a push off from the back foot with just the right force, and a good easy but quick bringing the head around. You can do a single without the arms. If your posture and turnout are secure, you can do a double without the arms.
When you get to triple and you use your arms, it will be easy. No strained neck, no shoulders creeping up.
When you come from a lunge, you're just covering more movement, and hopefully not losing your postural plumb line as you ronde de jambe en dedans to a la seconde and turn, releve and bring your foot into retire simultaneously and effect an easy spin. If you lose your balance, you need to practise without the turn until you get a strong releve maintaining your plumb line.
If these tours en dedans get really strong, it's nothing to do a tour en dedans in attitude. You've trained yourself to do a double without the arms. You've trained yourself to maintain a plumb line. Now you add changing your weight to a high attitude, and again, you can do this many many times without the turn, in between classes, to get that perfect position and hold it on balance.
You don't want to lose the feeling of spin - so try for as many turns as you can in class, within the parameters of the exercise given. And do the back-peddling to perfect your finer details, after class, with another student who will watch you, and get coaching from you for the same things.
If your buddy from class will hold the hand of your supporting side, and help you do some slow motion transitions from a lunge to your retire position, you can detect and correct anything going wrong.
The exercise lying on the floor, lifting the floor-side waist up to get the spine straight, and raising both legs slowly will strengthen the back and side torso muscles. This is where you need to be stronger, if you are not able to maintain the postural plumb line on your releves and turns.
I hope you'll try these exercisees in your daily routines, enhance the finer details, and create that muscle memory along with building strength. You will achieve optimum results for both quick sharp turns and the "floating" adagio turns that are so beautiful to behold.
Strengthen your work in ballet pointe shoes with this comprehensive dancer's guide.