Hi.Here is how to max your meter so you can practice combos and with enhanced moves and x-rays.
When in the practice mode after selecting your characters and you are ready to fight on the pause screen there are a number of options. so to change your meter so it stays at max all the time. access the pause screen by pressing start. Then press down twice and press A or X depending on which console you have. Then press down once and left once. You can then leave by pressing A or X and up twice and A or X or you can just leave by pressing Circle or B twice.