Crunch

The crunch is the most direct way to train the abs through their main job: flexing the spine. Lying on your back with your knees bent, you curl your ribcage toward your pelvis, lifting only your shoulders and upper back off the floor and keeping the range deliberately short so the tension stays on the midsection rather than pulling from the hips. It's a simple, accessible starting point for core strength that needs no equipment and can be done anywhere, which is exactly why it's so common — it's an easy first step for a beginner learning to feel their abs work. It does have real limits worth knowing: yanking on your head or neck to sit up can strain them, it trains only the surface-level flexion and leaves much of the deeper, stabilizing core untouched, and living on crunches alone can feed imbalances. Cross your arms or cradle your head lightly, curl rather than pull, and pair it with bracing work like planks. Used in that context, it's a fine tool for direct ab work.