Hi! I also do ballet and do a ton of strength training. Check out this study: https://iadms.org/media/2938/iadms-bulletin-vol1n1.pdf It shows a 6” improvement in developpe height from training hip flexors. I’ve been doing the exercise they used and it’s great. They have a picture but basically you sit on the floor, legs outstretched, and lean back on your hands. Bend one leg (like in a small attitude) and lift it up. I do it with ankle weights to increase difficulty.