What does the Modified Thomas Test measure?

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.

What causes tight hip flexors?

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.

How do I know if my rectus femoris is tight?

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.

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Hip Flexor Length Test

Use the Modified Thomas Test to measure hip flexor length, detect iliopsoas and rectus femoris tightness, and screen for anterior pelvic tilt risk.

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Hip flexor anatomy

Anterior pelvic tilt connection

Normative data & scoring

What to look for

Special populations

Limitations