Are your legs the same length?
Though you may not know it, they probable aren't. It's been estimated that up to 80% of the population has legs of slightly different length. This may never trouble you until you begin a program of vigorous walking, running, or high-impact aerobic dance, which can result in hip, back, leg, or foot pain. Generally the symptoms will occur on the side of the logner leg, because it's the one that absorbs an unequal share of the pressure. But the pain can occur on the other side, too. Legs of unequal length may cause immediate problems for a beginning runner, because the condition slightly distorts posture and thus affects the ability to withstand the pressures of running. If you weigh 150 pounds, your foot strikes the ground with 450 pounds of pressure when you're running on a level surface--more on a downgrade.
There are two types of leg-length differences. The first is an anatomical or structural shortening, perhaps caused by a leg fracture or by an inherited abnormality. The second is a functional difference: the legs actually are the same length but the feet hit the ground differently--most often one foot rolls slightly inward (called pronation), so that the leg is effectively "shorter." In either condition, the pelvis tilts slightly, twisting the spine and vertebrae and putting a strain on the ligaments in the back. There's some argument about how much of a difference is significant--some orthopedists say it takes a difference of at least 1/8 to 1/4 inch to cause problems, others say as little as 1/10 inch.
If you've stepped up your exercise program recently and are having hip, back, or leg pain, you should probably consult a physician or podiatrist. Indeed, anybody who's having back pain should have his legs measured. It's difficult, if not impossible, to measure your own legs accurately, but if one of your feet is excessively pronated, you may notice that when you put your feet together, your inside ankle bones are at slightly different heights. Or check the shape and wear patterns of your exercise shoes.
Sometimes X-rays may be required to measure your legs accurately, but a recent study in the journal Physical Therapy suggests that a professional who observes your gait carefully and uses a tape measure can make an accurate diagnosis. In most cases, the problem can be corrected with inexpensive shoe lifts (placed inside or on the outside of the shoes) or with specially prescribed orthotic devices. Orthoses--or orthotics, as these inserts are popularly called--should be fitted by a podiatrist or other experienced professional. Defending on what's involved, they may cost $400 or more. Some insurance polices cover them.