I believe Kivy has a module that deals with this. Though it is still(at the time of writing) experimental. Look here: http://kivy.org/docs/api-kivy.storage.html#module-kivy.storage
They appear to be using Pickle to store the data, according to this.
If that doesn't work for some reason,
what about using Pickle/cPickle yourself? If you don't know what those are, Google them now.
Then you could store user settings or workouts in a dict and pickle that dict, saving the
info to the sdcard as a simple text file, which shouldn't take up much space at all.
As far as I know, cPickle is a faster implementation of Pickle due to being written in C or possibly Cython, I am not sure. Hope any of this helps.
It's worth noting that it's possible to save text files to the Android device. I recently made a game with Kivy where I was doing just that, storing high scores in plain text.
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