Strong core doesn't just come from sit-ups, but from core exercises like planks. To build a strong core you need to do exercises that work various ab and postural muscles. Most people think of a strong core as a ripped six pack, but the truth is that the abdominal muscles are a very small part of the core. The core actually consists of many different muscles that stabilize the spine and pelvis, and covering the entire length of the torso. These muscles help control movement, transfer energy, shift body weight and move in any direction. Abdominal get all the credit for protecting the back and foundation of strength, but they are only a small part of what makes up the core. The fact is weak and unbalanced core muscles are linked to various of problems.
Working your whole core not just abdominals will:
-Reduce back pain
-Improve athletic performance
-Improves postural imbalances
-Help develop functional fitness.
Example of core exercise: Planks, Sliding pike, Oblique twist, Side balance crunch