Here is a simple but tough core strength (& endurance) challenge for you try. Knock out 40 consecutive “rolls” in the following sequence: 

• 10 cannon ball
• 10 can opener left leg
• 10 can opener right leg
• 10 mummy case (hollowed rockers)

Have fun with this one … and watch until the end for how to make this even tougher using dumbbells or kettlebells.