Kick your basic plank up a notch with this move to tone your core, glutes, and arms.
How to do it: Start on all fours with your hands under your shoulders and your knees under your hips. Keeping both arms extended (elbows soft) and pressed into the ground, extend your right leg back behind you and then bring the left back to meet it so that you are in a full plank pose (or the top of a push up position). Point your right foot off the floor and then bend your right knee into your chest, rounding slightly though your back and drawing your abs in tighter to lift your knee into your body. Next, flex your right foot as you press and extend your right leg behind you, into a back kick. Repeat 15 times on the right, 15 times on the left.
Bonus tip: Be careful not to arch your back as you perform the back kick. Keep your abs tight and your arms strong to maintain a strong plank position (avoid allowing your hips to sag to the floor) during the leg movements.