The hip is a complex ball-and-socket joint that includes a large number of muscle and tissue attachments from both above and below. Although runners more often experience pain in the knees and feet, hip pain can be debilitating. Owing to leg-length discrepancies and imbalances caused by factors such as uneven terrain, hip pain often occurs on only one side.
Piriformis Syndrome
One of the most common hip problems runners experience, piriformis syndrome occurs when inflamed or tight gluteal muscles impinge on the sciatic nerve where it courses through the butt. It is usually an overuse injury, and pain in your left hip may worsen with prolonged sitting. As this can result from an imbalance in muscle strength, you should see a physical therapist and undertake a conditioning program to strengthen the glutes on the left side of your body.
Iliotibial Band Syndrome
The iliotibial band, or ITB, is a tough band of tissue that runs from the top of your hip to the outside of your knee. Pain may occur in your knee, hip or both. The ITB stabilizes the pelvis, so an uncorrected imbalance leads to tightness and pain on the affected side. If your left hip is affected, the cause may be running too many counterclockwise laps on a track -- the usual direction -- or running facing traffic on a crowned road that tilts to the left. Icing, anti-inflammatory medications and keeping to level, flat surfaces can help dispense of this injury.
Overpronation
Pronation refers to the normal movement of the foot during the ground-contact stride phase, in which the foot rolls inward from the outer heel to the inner ball. Overpronation, which causes the arch of the foot to flatten more than usual, can result from poor footwear or unfavorable biomechanics. Pressure on the left arch can cause leg torsion extending up through the ankle and knee and to the hip, causing pain on that side. Replacing worn-out shoes and adding inserts to support the arch are usually sufficient to treat this injury.
Uphills
Hilly runs or hill repetitions helps you improve your endurance and develop more push-off power in the legs. Your butt and hip muscles are recruited to a great extent when you run up an incline. Unless you're on a treadmill, what goes up must come down, and as you descend, muscles that are already fatigued from the ascent experience a gravity-induced increase in impact stresses. If on top of this you run on an uneven surface, such as a trail, your chances of incurring an injury to one side increase.
