Hello,
I was wondering if there is a way to increase back flexibility once you're an ooooold ballet student (turning 25 soon

)
I'm actually very flexible in every part of my body (legs, feet, arms...), but would wish to be more flexible in the back, e.g. when doing cambré, arabesque (would like to be able to lift the leg really high), penchée, etc.
What would you recommend doing? I'm obviously not a professional dancer, so anything that might help w/o being harmful would be appreciated... Thanks!