This One Plank Variation Has Been My Core Kryptonite For Years — Here's How to Do It

• Start in high plank and bring your left knee to your elbow.
• Place your left foot back on the ground and repeat on your right side.
• Alternate sides, bringing your right knee into your elbow; place your right foot back on the ground. This completes one rep.
• Complete 10 reps.

For a variation that hits your lower abs, drive your knee across your chest to the opposite elbow. Repeat on the other side for one rep. Repeat for 10 reps.