Just have a question that I have just thought about, and was wondering if my chiro friends could help me. Does the anterior rotation of the pelvis seen in some athletes (due to hamstring injury and weak lower abdominal muscles) lead to a tight iliopsoas muscle group? I am at a lost to explain the tight iliopsoas muscle in any other way! 
reverse that…I tend to see tight psoas muscles causing rotation…then hamstring injuiries!
Then how does tight psoas muscles occur? It is simply by lack of stretching and flexibility?
yes, yes, and the psoas is used often in training.
Right. And when you refer to the iliopsoas, you’re actually talking about the iliacus and the psoas major. The iliacus attaches to the hip bone and the psoas attaches to the spine, explaining back pain in some situations.