Now, I am not a doctor, nor did I play one on TV, but this is what I came up with:
The oblique muscles are considered part of the abdominal muscles. They are located between the ribs and the pelvis and make up the waist. The obliques help the trunk to rotate and bend. There are the external obliques which are large muscles close to the surface of the skin. The internal obliques are deeper and situated right below the external obliques. These muscles can become strained due to a direct blow to the waist area, from overuse or forceful twisting and bending motions.
Bending or twisting the trunk in a forceful or improper way can lead to a muscle strain of the obliques. Grade one sprains usually require avoiding movements that aggravate the symptoms and may take two to three weeks to heal.
If some of the muscle fibers in the obliques are partially torn, then there is usually pain upon movement of the trunk and the area will be swollen and tender to the touch. The pain can be sharp, stabbing or burning and may get worse when twisting, performing sit-ups or when trying to lift the legs while lying on the back. Even gentle movement or stretching will be uncomfortable. This level of injury is called a grade two sprain and can take up to six weeks to get better. Rest, ice and medication to control the symptoms may be needed to help the injury heal. It will be important to return to activities slowly and only perform movements that are painless.
If the oblique muscles suffer a third-degree sprain then the muscle has completely torn or ruptured. Pain and muscle weakness will usually be severe. There may be uncontrollable spasms even at rest. The abdominal muscles may push through the muscle tear causing a hernia and internal bleeding. Surgery is often required along with months of therapy before returning to normal activities.