The following part is extracted from the link: http://en.wikipedia.org/wiki/Hip_flexors#Hip
It is about muscles which flexes the hip, and the muscles are listed below. And it says muscles are listed "in descending order of importance to the action".
Does it mean that iliopsoas muscle is the major muscle involving to flex hip and the muscle which applies lowest effort is Gracilis from the list. Does my interpretation correct?
The hip flexors are (in descending order of importance to the action of flexing the hip joint):
Collectively known as the iliopsoas or inner hip muscles:
Anterior compartment of thigh:
Rectus femoris (part of the quadriceps muscle group)
One of the gluteal muscles:
Tensor fasciae latae
Medial compartment of thigh:
Without the iliopsoas muscles, flexion in sitting position is not possible across the horizontal plane"