A routine exercise for strengthening extension is doing a developpe, lowering the leg 2 inches, and raising it up. Lowering, and raising it up. Basically, for as many times as you can stand it. Then, relaxing the muscles completely before doing the next position.
The assumption is that your placement is good, and you are not straining too much. You can do this lying down, (on your back for devant and on your side for a la seconde) to isolate the leg muscles, and then standing up, which is harder.
The repetitive flexing of the psoas muscles ( as in the above, not to mention every tendu and degage you do!) can leave those muscles strained and shortened with tension – so you need to stretch the psoas muscles – a lunge, in parallel, pulling up the abs and leaning into it gently and often, will stretch out the psoas. A deeper stretch is the runner’s lunge: one leg extended behind you, knee on the floor, palms on the floor on either side of your front leg; you remain pulled up as you stretch the psoas. If you turn sideways away from the back leg, you’ll feel a stretch along the TFL (Tensor Fascia Lata) which goes deep into the side of the hip muscles.
Lack of strength in arabesque could be in your mid back muscles, in your deep abdominal muscles, in your hamstrings, and in your hip extensor muscles.
Here’s a ballet exercise which will strengthen all those muscles. Stand in arabesque in the corner where you can hold one barre on the wall in front of you, and place the arabesque leg behind you on the barre behind you. Let the leg rest for a moment and check your placement.
Is the leg extended out away from you leaving you length in the back, as opposed to you having bunched up back muscles at and above the waist? Do you feel your butt muscles holding the leg as high as it can go? You can test this by lifting the leg off the barre without letting the back work or move forward at all. Just an inch, only the leg moves.
Hold the leg there, feeling the back of the leg (hamstrings) and butt (hip extensors) holding it. Put the leg down and pick it up 10 times, just an inch. Gradually work up to 20 times.
Here’s an extension of that exercise. Get placed like above. Do a demi plie, allowing your back to move forward as needed, but staying upright in your upper back. Lift the leg just off the barre and come up from the plie, holding the leg in position. Do this as many times as you can.
Always relax and stretch everything again after such a strenuous exercise. Tension leads to poor muscle tone=loss of strength.
For abdominals, lying down with perhaps a small rolled towel under your neck, super-slow motion pull ups are very effective. If you count three real seconds for the first inch of movement, and pull up slowly to count to ten; then, 3 real seconds for your first inch back down, and getting down on the tenth count – don’t relax! Repeat twice more before you rest back. That’s all! Only three times. You’ll feel those muscles really working. Breathe throughout – put one hand behind your neck if you feel a lot of strain (most do) and let the other hand reach out toward your knees. You only do this once or twice a week.
Here’s a wonderful stretch to oppose all that work – some call it a bow – it’s a yoga exercise. Lying on your stomach, reach back and grab your ankles – then lift up your feet and hands toward the ceiling and your body will make a bow shape. This will stretch those abs (including the psoas) and also stretch across your chest and the shoulder area. Don’t force to the point of pain – just enjoy a lovely stretch. You can stretch your back the other way by hanging over a large physio ball and just relaxing.
The above routines are very rigorous. If you do class daily I would only do these all, twice a week on top of everything else. If you do class two or three times a week, I would do them on those days (2 of them) because you are warmed up enough. But not two days in a row.