In reply to maybe_si:
> All the above is reasonably daft, just go running, wherever you live, doesn't matter and even with 2 small kids I'm sure you can find time for a run 3 or 4 days a week.
> Without doubt the best thing for it, if you live vaguely near a bit of a hill to run up then even better!
Second running. However, a heavy bag and the stairs is useful resistance training for the quads... as is spinning if you crank the resistance up a bit.