Psoas Stretch: 3 Hip Flexor Stretches & Anatomy -- Let’s find your hip flexors! From a standing position, lift your knee up toward your chest. The main muscles that contract to make this movement possible are the psoas, iliacus, and rectus femoris. The sartorius and pectineus also play a smaller but important role in flexion too (we'll cover those in a future video). VIDEO CONTENTS 00:11 Hip Flexor Tightness Check 00:42 Psoas Anatomy 01:22 Iliacus Anatomy 02:05 Why Your Hip Flexors are Tight? 03