Planks strengthen the upper, middle, and lower back muscles as they work to maintain proper spinal alignment and prevent the lower back from sagging or overextending, Marcotte says.

Planks are the ultimate test of total-body strength—not just your core. A personal trainer breaks down how to do proper planks and the muscles that planks work.

All of your body is interconnected, so the muscles work together and affect each other. Each plays a major part in your movements and posture. Muscle Health.