Cardio Step is a gentle workout to help your body maintain its aerobic fitness level without pushing you too deep into the fatigue zone. This is great as a workout when you do not feel like working out, or a program that will take you a step or two further into your fitness journey. Add EC for the extra load on your lungs and you've got yourself a workout that will work for you almost by stealth.
Extra Credit: 1 minute rest between sets.