Since I knew almost nothing about peripheral arterial disease (PAD), I jumped at the chance to talk with Dr. Michael Jaff a few days ago. He is the medical director of the Vascular Diagnostic Laboratory at Massachusetts General Hospital and a specialist in treating PAD.

Diabetes often causes it, and it is so often undiagnosed that only about one-fourth of the eight million people over 40 with PAD who have it know that they have this complication. PAD develops when the arteries in our legs become clogged with plaque -- fatty deposits and cholesterol -- and blood flow to the legs becomes blocked or limited.  Because those of us with diabetes have difficulty properly using the glucose in our food, the buildup of glucose in our blood can cause a change in our blood vessels that can lead to these circulation problems.

PAD can also cause chronic foot ulcers that can lead to amputations among people with diabetes. Those of us who have diabetes are at greater risk for severe PAD and are five times more likely to have an amputation than other people. But I wasn't the only one who knew little about it; awareness of PAD is in general low among those of us with diabetes.

When I interviewed Dr. Jaff, one of the areas I focused on was the role of exercise in preventing PAD by reducing plaque. It may well help.

"I haven't seen any studies demonstrating that exercise by itself reduces plaque," Dr. Jaff replied. "However, we clearly know that aggressive exercise -- predominantly aerobic exercise -- markedly increases HDL cholesterol, which is always good."

Aerobic exercise mean exercise that involves or improves oxygen consumption by the body. Aerobic means "with oxygen" and refers to the use of oxygen in our body's metabolic energy-generating process.

Walking, hiking, cycling, and snowshoeing are just some examples of aerobic exercise, all of which I like to do. I just resumed jogging after a lapse of about 20 years. Next, I will swim again. Variety is the spice of my exercise life.

But Dr. Jaff is concerned about anaerobic exercise and the risk of arterial disease. Athletes and body-builders in particular use anaerobic exercise to build muscle mass. When we train our muscles under anaerobic conditions, we get greater performance in activities of short duration and high intensity.

Resistance training or weight lifting are common names for this type of exercise. Now, after years of thinking that this would be boring, I am actually excited by a resistance training program for people over 50 that I began to participate in last month.

But it matters a lot how we do this type of exercise. "I have some concerns about isometric exercise and the risk of arterial disease," Dr. Jaff told me.

"The reason I say that is often people who do a lot of weight lifting -- especially with higher weights and fewer repetitions -- put too much stress on the endothelium." Dr. Jaff is talking about the thin layer of cells that line the interior surface of our blood vessels.