With aging, it takes more effort and time to walk up stairs, mow the lawn, fix a faucet or wash the dishes. Tasks that you did without effort when you were younger can become major ordeals that leave you exhausted when you are older. Dr. Jerome Fleg, a cardiologist at the National Heart, Lung, and Blood Institute, tested 800 men and women over several years and found that their ability to sustain exercise decreased rapidly as they aged. The older they became the faster they lost what researchers call aerobic capacity (Circulation, July 26, 2005).

Aerobic capacity is a measure of your ability to use oxygen to do work. If your body can process more oxygen than that of another person, usually you will be able to run faster, walk or work longer, and have more energy than that person. The men and women lost three to six percent per decade in their 20's and 30's , and 20 percent per decade in their 70's. The men lost aerobic capacity faster than the women. The men lost 8.3 percent of aerobic capacity in their 40's and 23 percent per decade in their 70's.

This study was done with people who were healthy enough for vigorous exercise on a treadmill that measured their exercise capacity. People who have had heart attacks, strokes, diabetes or other wasting diseases would lose aerobic capacity much faster than healthy people. The results showed that a regular exercise program can increase exercise capacity by up to 25 percent, which would give the older participants the same exercise capacity as you would expect in people who are twenty years younger.

The loss of aerobic capacity with aging explains why older people cannot compete effectively against younger ones in endurance events. The good news is that a regular exercise program can increase your maximum heart rate. By exercising regularly and vigorously, your will develop stronger skeletal muscles. When you contract your leg muscles, they squeeze against the veins in your legs and pump blood toward your heart. When your leg muscles relax, the veins dilate and fill with blood. This alternate contacting and relaxing pumps extra blood toward your heart. The extra blood returned to the heart stretches and strengthens the heart muscle, causing it to beat faster and with more force. So strengthening your leg muscles increases your maximum heart rate, even as you age.

Gabe Mirkin, M.D.

Dr. Gabe Mirkin has been a radio talk show host for 25 years and practicing physician for more than 40 years; he is board certified in Sports Medicine and three other specialties.

Dr. Mirkin's daily features on fitness have been heard on CBS Radio News stations since the 1970's. He has written 16 books including The Sportsmedicine Book, the best-selling book on the subject that has been translated into many languages. His latest book is The Healthy Heart Miracle, published by HarperCollins.

Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. A Boston native, Dr. Mirkin did his residency at the Massachusetts General Hospital. He has served as a Teaching Fellow at Johns Hopkins Medical School, Assistant Professor at the University of Maryland, and Associate Clinical Professor in Pediatrics at the Georgetown University School of Medicine. He has run more than forty marathons and is now a serious tandem bicycle rider with his wife, nutritionist Diana Mirkin.