Some people have the idea that they have to run on the treadmill (or outside) for 30 minutes to an hour to get an effective workout. Well luckily this is not true; my personal trainer a few years back shared with me the fact that after 45 minutes of intense cardiovascular exercise, you actually stop burning fat and start to burn your muscle...not good.
All you need is 20-45 minutes for an effective cardio workout. But when you do HIIT (high intensity interval training) you can get an amazing workout, and great results over time in just 20 minutes.
Here's the workout:
Follow this routine and I guarantee that you will be dripping sweat by the end of the 20 minutes.