Eager to lose weight many times people over train and the end result is extremely sore muscles and in some cases injury.  When this happens people quit exercising all together.  So be sure to listen to your body and take a couple of days off to allow your body to recuperate.  Also start off slowly with 10 min., then 15 min., slolwy working way up to 30-45 min. of cardio 3-5 x per week.