Mula bandha (the root lock in yoga) is a way of using your pelvic floor muscles to bring your practice together in nearly every way. It will help you protect your back from injury when doing backward bends, and make your inversions and arm balances easier to get into and maintain.
What is the Psoas?
For those in the know, few muscles in the human body elicit as much interest as the psoas! The psoas is a rope-like muscle located deep in the belly, which starts at the lumbar spine near your lowest ribs and runs to the inside of your femur. The psoas is joined at the hip by the iliacus, which travels from hip to thigh. Together, the psoas and iliacus make up the iliopsoas–your body’s most powerful hip flexor.