DEAR DOCTOR K: My right calf starts aching when I exercise. My doctor said she wants to do a test that is like taking my blood pressure in my leg instead of my arm. Does that make any sense?

DEAR READER: I can understand why that seems confusing, but your doctor is right. She is probably worried that the arteries to your right leg have blockages from plaques of atherosclerosis. When you exercise, your leg muscles need more blood; it provides the nutrition they need to work. When blockages prevent your leg muscles from getting the blood they need, they scream in pain.

The leg pain caused by atherosclerosis is usually felt in the calf, though sometimes it is felt in the thigh. Typically, the pain starts only after a person has been exercising his or her legs for a while. When a person stops exercising, pain caused by atherosclerosis typically goes away over the next minute or two.

Of course, many different conditions can cause leg pain when we exercise. In particular, injuries to leg muscles or to the hip, knee, ankle or foot can cause exercise pain. Just from your symptoms alone, it is hard to be sure what is causing leg pain when you exercise.

A key test for problems in peripheral arteries is the ankle-brachial index, or ABI. An ABI compares blood pressure readings from the ankle and the brachial artery, which is the major blood vessel in the upper arm. The test is done using a blood pressure cuff and an ultrasound probe.

Normally, blood pressure is similar whether it is measured in the legs or in the arms. If blood pressure is lower in the legs, it usually means that fatty buildup inside the leg arteries is interfering with circulation.

The doctor will calculate your ABI by taking the highest pressure recorded at your ankle and dividing it by the highest pressure recorded at your arm. The normal range is between 0.90 and 1.30. A result under 0.90 means that blood is having a hard time getting to the legs and feet. The lower the number, the higher the chances of leg pain while exercising or of limb-threatening low blood flow.

The ABI also offers information about your general cardiovascular health. An ABI result under 0.90, for example, also indicates an increased risk of heart attack, stroke or dying of heart disease. That’s because people with severe atherosclerosis of the arteries of the leg usually also have atherosclerosis of the arteries of the heart and brain.

A recent study estimated that about 20 percent of adults older than 55 have blockages in the leg arteries, although not all of them have symptoms yet. Not surprisingly, the problem is even more common in people who have risk factors for atherosclerosis. That includes smoking, untreated high cholesterol, untreated high blood pressure, diabetes, or people in your family with a history of heart attacks, strokes or blockages in the arteries of their legs.

I hope your test goes well and that the result is reassuring.

(This column is an update of one that ran originally in September 2013.)

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.