Q: How do you get a high arabesque leg with your back perfectly upright? I know I have the flexibility to have an arabesque over 90 degrees, but can't seem to get my leg up there.
A: There are two things you should focus on for a beautiful arabesque: first, having flexible, strong muscles at the hip, and second, having strong core and upper-back muscles so you can maintain that elegant lift of the spine.
If you know you have the flexibility at the hip and can easily do the splits, perhaps there is some weakness in your hamstrings and gluteal muscles. Check this by noticing how hard it is to do the bridge exercise with both feet on the floor, and then slowly lift one foot off the ground without letting the pelvis drop to one side.
Next, check your spine. Round down into a halfway standing forward fold, but bend your knees slightly to take the strain off the hamstrings. Then have a helper look at the shape of your spine as you are folded over. Is it in a C shape? If so, you have good flexibility in all three areas of the spine. Is the area between your shoulder blades or lower back flat? The flattened areas may indicate muscular tightness. Do you tend to slump at the desk or computer? If so, strengthening may be useful for your upper middle back.
A great exercise is to first rest on your back over a big physioball in order to give your middle back muscles a rest in an extended position. Then turn over on your stomach and place your hands behind your head with your elbows out to the side. Slowly lengthen your spine to lift off the physioball, while keeping your core engaged and on the ball so you don't arch into your lower back.