If it hurts to touch a point that's in the middle of one side of your buttocks, you probably have piriformis syndrome. This chronic condition is very difficult to diagnose, because other injuries may produce exactly the same symptoms. Similar pain may be the result of an injury to bones, muscles, tendons, bursae (pads between the tendons and bones), the hip joint, or the sciatic nerve, but there are ways to determine from which condition you might be suffering.

If you feel most pain when you land after hopping on one leg, you might have an injured hip joint or a stress fracture in your pelvis or upper leg bones. An x-ray will usually reveal a joint injury, but only a bone scan will reveal a stress fracture.

If you feel pain in your buttocks, particularly when you touch your toes while keeping your knees straight, you might have a tear in the large muscles or tendons that run down the back of your hips.

If you feel pain when you touch a spot that's either on the lowest point of your pelvis (the part that touches a chair when you sit) or at the top of your femur (thigh), you might have injured your bursae (bursitis) or torn the tendons that are attached to bones at these sites.

If your back hurts, particularly when you bend backwards, and the pain goes down the back of your leg to below your knees, your sciatic nerve is probably being pinched in your back.

Cause: The sciatic nerve is the longest nerve in your body. It starts on the lower part of your spine, [passes through a hole between the piriformis muscle above it and several other muscles beneath it, and goes down the back of your leg to below the knee. When you run, the piriformis muscle contracts and squeezes the sciatic nerve underneath it. Repeatedly squeezing and relaxing the piriformis muscle can damage the sciatic nerve and cause pain. This injury is thought to be caused by an innate tightness of the piriformis muscle or a structural abnormality in the path of the sciatic nerve. It can't be attributed to a specific error in training.

Treatment: Priformis syndrome won't ease until you stop running. Don't run again until you can run without feeling pain in your buttocks. If it hurts to touch, it hasn't healed.

In most cases, pedaling a bicycle will also be painful. You probably shouldn't do any exercise that causes you to bend at the hip while keeping your knees straight, because this will stretch the sciatic nerve. You might be able to swim, if it isn't painful. Medication doesn't usually alleviate the pain, and even if it does, the pain will return as soon as you stop taking it.

Sometimes, the pain will disappear after a rest of a few days to several months; frequently it does not. In this case your doctor will be able to make an accurate diagnosis by injecting a mixture of xylocaine and corticosteroid drugs directly into the piriformis muscle where it passes over the sciatic nerve. If the pain disappears, you may resume running only after a few weeks, but remember that this injury tends to recur. If you feel pain in that area, stop running immediately, and don't attempt to run again until you can do so without pain.