Begin in the basic plank position. Your torso will be in a straight line from head to toe and avoid any drooping or sagging of the hips or shoulders. Also avoid arching your back, or hanging your head. Warm up by maintaining the plank for at least 60 seconds while maintaining control. If you start shaking or losing form, drop to your knees and rest a few seconds and continue until you've completed a full minute
If the basic plank is too easy, after 60 seconds, add a few arm and leg lifts to the next 60 seconds. Every 15 seconds, alternate lifting one arm out in front of you while maintaining your posture for 10 seconds and repeating on the other side, and then switch to the legs. Lift the toes 5-10 inches off the floor and hold it for 15 seconds, and repeat with the other leg.
After completing this two minute exercise, your core should be thoroughly warmed up.