One of the crucial abilities in gymnastic tumbling is the ability to pull your knees into your chest and make a ball: The Tuck.
If you cannot, or won’t, ‘Tuck” your tumbles will be open, slow and difficult to land.
This means that you must get your calves to stick to your hamstrings and your knees to your chest with a rounded back . The G force of most tumbles will try and rip this shape apart. Make sure you can squeeze the tuck both through body control ( abs, chest and leg compression) and by pulling your knees in by grabbing your upper shin’s. As much time as you spend dish and arching, allocate to the tuck, especially if you are open and lazy in your front and back tuck. On the whole, get this shape with the head sort of neutral, not massively strained back ( you are preparing for both a front and back tuck).
If you were taught the basics properly, you will be used to this position in your forward rolls. As an adult, most gymnastic teachers will shy off demanding that you properly tuck in your rolls, and thus leave you unconditioned. The forward roll will put you into a tuck by the nature of the move, but its more a “flop into place tuck” than one you have worked for. I’ll post more later, but hold that tuck in a variety of positions.