Besides doing middle splits, you can do this one which works really well. Sit in a stradle. Stretch your hands out in front of you, but do not touch the floor. Lift both of your legs up and bring them down to about two inches off the ground. Repeat.
You can also do an excercise where you put a double rubberband (thich ones) on your ankles and do toe-touches with it on. When you take it off, your jump will be better.
For a double:
The only thing that you can really do to help make you spin faster is to practice spinning. On the trampoline, in the air, into a pit, ect... You can do one excercise though. Lay flat on your back. Put your arms in a tee, lifted slightly off the floor. Practice yanking your arms to your chest or to your side really quickly and bring your whole body to the side. This will teach you that you have to keep your abs tight and really use your hips to get around.
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