Here's how to join the challenge:
1) Video: Every time you start your workout, watch all the days leading up to the day you're on, following along with the exercises. For example, on Day 1, you'd do the plank. Day 2, it's the plank + 6 supermans. Day 3, you add on 3 kneeling sit-ups. By Day 21, you'll be doing all 21 exercises. Phew!
2) Chart. Pin this chart, or bookmark this page, and follow along below. You'll find descriptions of all the exercises in the video.