Lots of people think their core is their abs but that is a big mistake. The core muscles include transversus abdominis, rectus abdominis multifidus, internal and external obliques, also include longissimus thoracic and diaphragm. You can consider the core as everything on your body minus the arms and legs.
I recently helped one patient with severe back pain. He did not do exercise very often, worked long hours in front of the computer, which caused his core to become weaker over time. He tried to lift something heavy and triggered the pain.
We originated most full-body functional movement through the core. A strong core gives you better posture and balance, will prevent and reduce back pain and improve the overall quality of life. I always do the following exercise when I have time to strengthen my core.
1. The Plank
Rest forearms on the floor with elbows directly underneath shoulders and hands facing forward. Then extend your legs out behind and rest your toes on the floor keep your body a straight line from shoulders to heels. Make sure you are not dropping your hips or hiking your butt up and keep your neck in a neutral position.
(Image from https://www.womenshealthmag.com/)
2. The Panther Shoulder Tap
Start on all fours and engage your core. While keeping your back flat and
your butt down, lift knees off the floor about 1-3 inches. Then start to tap
your right hand to left shoulder, and then alternating side.