Do not work out for your "health" or by dietary theories (which are largely based on Western dietary habits anyway). Work out to understand how Flow can be expressed beyond typing at a keyboard. (Consider that in most contexts where we talk about "Flow," studies involve sedentary activities: playing video games, typing/programming, flying a simulator or an actual air-vehicle, driving, etc.) What is with the given assumption that Flow involves Hands/Brain? Why not Feet/Brain? Imagine being able to establish Flow immediately while engaged in a physically exhausting activity. How far will you go? For how long will you play?
In short time, your body will naturally develop into the kind of fitness appropriate to the limits of your mental limitations. Moreover, you may develop a grammar for your feet which is analogous to the grammar of your hands (in the context of a keyboard -- consider that we all type relatively uniquely to ourselves, a typolect, if you will, despite "Standardized" keyboard formats; in the context of vim -- verbs, nouns, modifiers, sentences, paragraphs, etc.): Foot Grammar (might allow for "propositions" of the foot which demand a fitness level (performance criterion) to express them.
You type through the pain of the monitor against your eyes. You type and think through fluorescent lighting. Carpal Tunnel. Etc. This is why we suggest getting up and stretching, walking about, to combat these minor physical impairments which involve attrition over time. So many physical analogues exist which naturally make playing futball a sensible, and moreover social (!), activity for programmars.
I type through wrist pain and learn a new framework. I kick through foot pain and learn a new tactile passing system.