I like to alternate my cardio workout every time. I do treadmill for interval sprints, stairmaster, elipticals, rowing, and occasionally swimming.
What I like most is to cycle in the mountains surrounding the town I live in. Nothing beats a high and steep hill taken at high speed, followed by a resting pause while driving downhill at lunatic speed. Love it.
All you have to to is walk ...the key is to keep an elevated heart rate for a sustained period of time....If you go above that by and do it too much then you will also burn muscle.
When I pre pare for a show the only thing I do is walk on the tread mill starting 4 or 5 weeks out, and so does everybody else I know in preparing for a show My training partner looses about 35 lbs going into a show and all he does is walk, but he works up to 1 hr a day of cardio too...that sucks