All you do is push forward the joystick. Check your characters weight. If its looks like 230/200 then you need to lose some items. If the numbers on the left are higher than the right, you need to get rid of/sell some junk.
Indeed, it's the combination how much you push of the anolog stick, your carry weight and weather you have your weapon ready or not that determines your speed. If you are overburdened, you are limited to the slowest pace...