Your core muscles work to stabilize the spine and hips and include the abdomen, back, glutes and upper legs. A strong core is key to improving your mobility, balance, posture and strength. Most of us think crunches and other exercises done while lying in a supine position are best for increasing core strength. This is a common misconception. In fact, the entire core must be engaged by incorporating a wider range of motion to get the most benefits from your workouts.