The iliacus and psoas muscles come together to form the iliopsoas muscle. This is a very important muscle when it comes to us modern humans, since we all tend to work very hard at inadvertently shortening this muscle.
Sitting, which we'll all be doing a lot more of in the coming weeks or months is very detrimental to the human body, especially the spine. This is not just limited to the lumbar spine as most of us tend to think, but the entire spine. From the neck down, sitting is a long-term boon to good posture and proper muscle development, joint articulation, and ligament health.
This is something we've compared to smoking before. It really is that bad. And now with the fallout from the Coronavirus pandemic, we are more resigned to our chairs and couches than ever.
Here is a short and sweet video about the Iliopsoas Stretch