Hip Flexor Length Test

It measures the length of the two main hip flexors. The thigh angle reflects iliopsoas length, while the knee flexion angle reflects rectus femoris length. A thigh resting at or below horizontal with the knee bent to about 80–90° indicates normal length.

Prolonged sitting shortens the iliopsoas, while heavy quad-dominant training can tighten the rectus femoris. Tightness pulls the pelvis into anterior tilt, which can contribute to lower back discomfort and reduced glute activation.

If the hanging knee stays extended beyond 90° of flexion, the rectus femoris is likely tight. When the thigh sits at horizontal but the knee will not bend past 90°, the restriction is coming from the quad rather than the iliopsoas.