Your body’s core—the girdle of muscles, bones, and joints that connects your upper and lower body—gives you stability and helps power the moves you make every day. Whether it’s bending to pick up a laundry basket, paddling a kayak, or reaching to pull a vase from the top shelf of a cabinet, a strong and flexible core makes the move more fluid, efficient, and robust. Strong, well-balanced core muscles can also improve your posture and help prevent back injuries. Exercise and fitness programs increasingly focus on the core. Lunges, squats, and planks (a move that looks a bit like a push-up and is often substituted for sit-ups) are key moves in most good core workouts. But it’s important to pay attention to proper form to protect you from injury and help you gain the most benefit from each exercise.