Hi! I have long hair too (about to bellybutton), although mine is quite thin.I found it REALLY irritating at practice, especially when twisting-it would always swing and whack me in the face. Or it would get caught under my hand when I did giants-owch!And, if I tried the half-ponytail, it would just fall out and tangle. Sorry. I will stop my rant now and try to be helpful. I've found 3 hairstyles that really help me, and I am about as girly as the sky is red, so if I can do it- anyone can.
1)Okay tie a ponytail, and make it low-ish. Then, take one of those hair clips that have that metal clasp in the back ( the clasp is like this
Link Removed ). Pick up the ponytail and put it against your head, so the ends of it are up, (going over your head and into your face). Use the clip to secure the ponytail to your head a few centimetres above the first elastic. Then, tilt your head back and wrap an elastic around the newly formed, higher-up ponytail. I really hope that makes sense, if not, I will post a picture. It helps to sort of shorten your hair.
2) This one doesn't really shorten, but it helps keep your hair in place and doesn't fall out. I found a random youtube vidoe that explains it pretty well:
Make your hair look longer WITHOUT EXTENSIONS ! - YouTube
I know it says "make it look longer", but it's a good hairstyle for practice-just ignore that part.
To modify for gym- If your hair is really long- do 3 sections instead of 2, and instead of the whole bobby -pin thing just use a hair elastic to tie the 2 parts together.
3) This is the last one
Gymnastics Hairstyles - Nastia Liukin Inspired French Braid Ponytail - YouTube
This one is kind of tricky, but try it- it really helps, WILL NOT fall out, and is good for meets!
Good Luck! Sorry about the length!