Here is a core circuit routine guaranteed to get your abs pumping! PERFORM PER ROUND: 20 sec  – Crunches 20 sec – Leg Lifts 20 sec  – Russian twists 20 sec – Elbow Plank Rest 45 sec -1 minute between rounds. NUMBER OF ROUNDS: Beginner – 5 Intermediate – 6 Advanced – 7 Your Gymboss Classic Interval Timer makes a perfect…