Our heads are like bowling balls  — big, round, and heavy. When the head is balanced directly atop a healthy, erect spine, it requires less effort for your neck and back muscles to support it. Poor posture can cause back, neck, and other muscle and joint problems. As you slump, your body may compensate by flattening the normal inward curves in your neck and lower back. This can cause pain and degenerative arthritis of the spine.