Hip flexors

In anatomy, flexion (from the Latin verb flectere, to bend) is a joint movement that decreases the angle between the bones that converge at the joint. For example, your elbow joint flexes when you bring your hand closer to the shoulder. Flexion is typically instigated by muscle contraction. A muscle that flexes a joint is called a flexor.

The hippie flexors Vesi are (in descending order of importance to the action of flexing the hip joint):

Without the iliopsoas muscles, flexion in sitting position is not possible across the horizontal plane.

...
Wikipedia