A frequent source of lower-back pain comes from two muscles you might not have heard of—and that makes sense since you rarely see them on those medical posters of human anatomy in doctor's offices.

Leaf through a textbook, watch a wellness influencer, or listen in at the gym, and it can feel as though the human body has already been mapped to exhaustion. Every muscle named, every nerve traced.

The human body is composed of more than 600 muscles, all of which are very important for movement, strength, and balance. However, among these many muscles are some that are quite large and strong, ...