Begin in an elbow plank position with a small, folded towel or paper plate under each elbow. Keep your elbows directly under your shoulders, back flat (neutral spine) and core tight!
Slide your right elbow forward until your arm is nearly fully extended. With control, bring the right elbow back to center.
Repeat on the left side. This completes one rep. Start with 10 reps and work your way up to 20!
If you need to modify, you can drop to your knees (while keeping your back straight and core tight); you'll still work the core and triceps!
You will be shocked by how intense this exercise is on both your abs and arms. But don't throw in the towel (see what I did there?).