I have been told running is the best cardio exercises. It is also the cheapest. It's perfect for me cuz I don't want to donate spend money on gym memberships, yet get an effective workout. So, I did some reading and found that the best training program which I can do on my own is the Couch to 5k running program, which over a course of 9 weeks train you to run 5k's in approximately 30 minutes.
