I am a fan of pyramids (see thigh pyramid workout). If you played any sports in high school you might remember them (fondly or maybe not so fondly) as ladders. Basically, you start with a short interval (for this workout it’s 20 seconds), and work your way up (climb) to the longest interval (50 seconds) and then you step easily back down to the short interval again (20 seconds).
All the intervals here are less than a minute. This makes the time fly and boosts your motivation as you see the intervals get shorter as the end of the workout gets closer. No equipment is necessary for this workout except an open space in which to do it. Turn on some good music and you’ll get a full body cardio/toning interval workout!