The most common condition resulting from a tight psoas muscle is back pain. When your psoas is tight and you are standing up, the contraction of the muscle brings the lower back into a greater than normal degree of arching. This arching of the lower back compresses the vertebrae and brings all of the lower back muscles into a shortened state. The result is muscular tension and pain, disc problems, sciatica, and a tendency to throw the lower back into spasm. A tight psoas muscle also causes or contributes to a number of other conditions, including hip pain, groin pain, uneven leg length, scoliosis, instability in the core of the body, and limited flexibility in the lower back.