How to do the Hundred with proper form How to: Lie on your back with your knees bent, feet flat, arms at sides. Lift your legs to tabletop (90 degrees at hips and knees) and engage your core.

Follow these form cues to learn how to do a perfect plank. Once you've read the step-by-step directions, follow along for some higher-level tips from Samuel to dive deeper into the exercise.