Your core has more than one side to exercise.
Many core exercises primarily target the front of your stomach, i.e. your abs. Now, I’ll be the first to say having a six pack is awesome, but if focus exclusively on your stomach, the rest of your core is going to miss out. In addition to have strong abs, you want firm hips, a strong back, tight glutes, and a bunch of other core muscles whose names I can’t remember off the top of my head. Ergo, you need to go at that core from every possible angle, not just the front.
For example, a set of landmine rotations, wherein you attach one end of a barbell to a firm surface (or a landmine attachment on a rack, if you have one) and rotate the other end toward yourself. This exercise is great for your abs, of course, but due to the sideways angle of it, it’s also good for your sides and hips.
If you’ve got a resistance band, you can attach it to a rack or other solid stationary surface for a half-kneeling hand pallof press. With one knee on the ground, press the band out in front of you, being careful to synchronize your breathing to the pulls. Since this exercise involves kneeling, it’s great for your lower back.
If you want to get outside and get some air, try a suitcase carry. This requires the least equipment; just get a comfortably heavy dumbbell and let it hang down in your hand. Keep your abs tight and your spine straight and upright and walk a reasonable distance. You’ll really work your mid back with this one.
Think of your core like a cube. A cube has multiple angles and multiple surfaces. If you expanded only one side of the cube, it wouldn’t be a cube anymore, would it? It’d be a rectangle. So make sure you go at your core from every possible angle so you don’t end up a rectangle.
