Plank HIIT Workout – Core HIIT Series (Plank & Stability Part 2) Planks aren’t just about holding still — once you add movement, your core has to fight harder to stay strong. That’s where this plank HIIT workout  comes in. In Part 2 of our Core HIIT Series, we’ll push your abs, shoulders, and obliques with three dynamic plank variations that will challenge strength, balance, and stability in just 10 minutes. The Workout Format: 40 seconds work per move 20 seconds rest between