You need to start with a warm up of light stretching or walking in place while rotating arms and trunk. NEVER lock elbows or knees while working out or stretching. Save the static stretching (holding for 20 seconds) until the end of workout session. Also try to reach and maintain Target Heart Rate.
To calculate THR: 220-age will equal Max heart rate. Take that number and multiply by 65% for beginner, 75% for Intermediate, and 85-90% for Advanced.
REPEAT Circuit at least twice. TRY FOR 3 ROUNDS!