Extra Crunch takes one simple exercise and makes it harder through repetition. Because the rest periods are short, your abs have to keep working before they have fully recovered. That is what makes this more than just a floor add-on. Each round of crunches becomes a test of core endurance - your abs have to keep contracting with control, while your neck, hip flexors and momentum stay out of it. Focus on curling your ribs toward your hips rather than pulling your head forward, and keep each rep clean rather than fast.

What this builds is better control of your core. The main abdominal muscles handle the curling movement, while the deeper core muscles work to keep everything steady and neat. Done with control, this improves your awareness of how your core works, the quality of each contraction, and your ability to create tension without big dramatic movement. That carries over into stronger planks, better sit-up patterns and a more connected feeling through your whole trunk.

Four rounds. One exercise. Surprisingly effective.