Health & Injuries: I’ve recently started a more aggressive training schedule with longer runs. The day after a long run (7-8 miles), my left hip started hurting. It’s very stiff and sore, especially after I sit, but feels better when I run.  It’s a little sore when I press right behind the hip bone or follow it straight down to my upper leg.  The buttocks hurts a little, too.  I’m not sure if this is the piriformis muscle?  Do I need to take a break from running or see a doctor?  Thanks for your advice!

Your description of hip pain seems to localize the problem to the outside of the hip and the left buttock.  I am guessing that when you press behind the hip bone you are pressing on the boney prominence on the outside of the femur (thigh bone) known as the greater trochanter. The piriformis and other muscles in the buttocks attach to this area.  The iliotibial band runs over this prominence. Inflammation of the piriformis or IT band could cause your symptoms.  Since your pain improves when you run, more serious problems are much less likely.

The increase in training is creating new stresses on your body. Strength and flexibility deficits will become more obvious as the body is stressed. I would recommend working on core and hip strength and flexibility. Check out the articles on this website on IT band problems and piriformis syndrome  for some exercises to get you started. As long as you are not having pain while running and the problem is not getting worse, you may continue running, though I would not increase your workouts until the symptoms subside. Apply ice to the painful area for 15 minutes following your workouts. If symptoms do not improve or they get worse, see your physician.