Begin in an elbow plank position with a small, folded towel 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 centre.
Repeat on the left side. This completes one rep. Continue alternating for 30 to 60 seconds.
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!