What is a great free ab workout routine?

A great abdominal workout routine consists of various movements that engage the core muscles. Intervals of quick, fast paced movements and slower, concentrated movements returns optimal results for a flatter stomach. Planks, crunches, sit-ups and other variations of abdominal movements make a great, free routine.

An example of a great abdominal routine is to first warm up the body's muscles by doing five minutes of walking in place while lifting the knees as high as possible. Once the body is warmed up, do an alternation of a sit up then standing up ten times in a row, planking for thirty seconds, ten crunches, ten reverse crunches, ten heel touches, ten leg raises, planking for thirty seconds again, and then repeat the entire circuit three times.