Viva prep is a series of tasks and activities that help you towards being ready for the specific challenge of your viva. From that perspective, I think it’s fair to think of it as a workout: you’re exercising specific mental muscles, getting in a good academic condition for the work you’ll do on the day responding to your examiners.
Viva prep is building on foundations you’ve created through your life and PhD journey; like many workout programmes it requires a little preparation itself, a little planning so that you space the work out.
(no pun intended)
Like a workout though, you have to actually do the work. You have to read your thesis, make notes and annotations, rehearse for being in the viva and more. And like a workout that work is personal to every candidate: every candidate has a unique set of needs they have to satisfy to reach the ready state they want, even if there are general principles that will help every candidate as they work towards being ready.
So: what are your needs? How are you going to workout in preparation for your viva?