The Psoas muscle starts from the front of the spine and works its way through the abdomen, over the front of the pelvis and attaches to the front of the femur. This tortuous route means it has to run and rub over the front of the pubic bone. This run is cushioned by a bursa but typically it can become inflamed when the muscle is overworked or is tight.
This presents as a deep sore pain in the front of the hip, quite deep but very tender when you find the sore bit. It is ok to rest but can be sore to get going and particularly to run or cycle.
There is a lot we can do with these from the local mobilisation of the tight muscles, the mobilisation of the sacroiliac joint and the pelvis which can be the cause of the problem as well as associated nerves and other muscles alongside such as Iliacus.