The psoas major and the rectus abdominis muscles have an important relationship inside the body even though they don’t literally work together. Muscles relate to each other in many different ways. Sometimes they work in opposition—for .
The number one cause of lower-back pain is a tight hip flexor (or psoas). It happens to everyone and is usually caused by sitting down; another cause is sleeping on your side in a fetal position. back pain dolor de espalda