I have been doing this workout for almost 2 years now and I love it because it only takes 20 minutes, 2-3 times per week. Anyone can do this because it can encompass any physical activity level. You can incorporate this workout with fast(er) walking, running, biking, elliptical, treadmill, etc.
The method is:
00:00-03:00 3 minute warm-up (pace of 3 to 4.5 mph, depending on your stride)
03:00-17:30 Followed by 8 of these pairs of activity :
1.) 30 seconds of intense activity of choice (fast walk, run as fast as you can, biking as hard as you can, etc.) 03:00, 05:00, 07:00, 09:00, 11:00, 13:00, 15:00, 17:00
2.) 90 second recovery period (same pace as warm-up)03:30, 05:30, 07:30, 09:30, 11:30, 13:30, 15:30
17:30-20:00 2.5 minute cool-down period (the same pace as warm-up)
Do not do more than 2 - 3 times per week!
Weight train on alternate days to build muscle using anything you have handy (water bottles, canned goods, weights, etc.).