This refers to exercise induced leg pain caused by muscle swelling within the anterior (front) compartment in the leg. The compartment is the tough fibrous bag around the muscles and when the muscles in the compartment swell the pressure can rise and reduce the blood supply getting to the muscles and nerves. The lack of blood supply then causes pain. The deep compartment lies just to the outside of the shin bone. Compartment syndrome can be caused by rapid increases in the size of the muscles associated with significant increases in training (often seen in military recruits), or unaccustomed strenuous exercise.
You will feel pain along the lower outside edge of the shin. It is often described as an ache, or tight cramping pain, this may be associated with pins and needles between the first and second toes. The muscles there may feel hard and tender. It comes on soon after starting exercise and goes shortly after stopping exercise. When the problem becomes severe it will stop you exercising. Deep massage and icing can help with the symptoms but do not offer a lasting cure.
If you think you have this condition it is well worth getting it checked as soon as possible by Mr Willis-Owen. You should avoid any aggravating activities which may make things worse. It will not get better on its own, unless you significantly alter your activities.
Treatment involves first confirming the diagnosis and excluding other problems such as tenoperiostits or stress fractures. MRI scanning or bone scanning are helpful to exclude these and are best done when the pain is bad (Mr Willis-Owen may ask you to train hard for the few days before the scan). Compartment pressure testing is needed to confirm the diagnosis. This involves putting a needle into the compartment to measure the change in pressure when exercising. Surgery to release the tight compartment is often needed in severe cases and correcting any biomechanical problems is also helpful.