Sometimes you should listen to that little voice inside you, but almost always when it's saying "oh I dunno, we don't really have to go for a walk do we?" or "okay five blocks is enough right?", it should just be ignored.
I'm not talking about the voice of your injured knee or something like that; I mean the inner grub that just wants to sit on the couch wiggling its tail at the TV and shoving nachos into its maw.
"Ewww, grubs!" I hear you say.
Damn straight. Ick.
Walk an extra 10 blocks before lunch, it won't take you long at all and it's good for you to shake a leg. While you're at it, tell the grub to shut up and choose something healthy for lunch that won't throw you into an afternoon food coma.