It may not be too late to benefit from exercise, even for people in their 60's and older, according to scientists at the National Institute on Aging (NIA) Gerontology Research Center, the Johns Hopkins Medical Institutions, and the Veterans Administration Medical Center, Baltimore. They find that an aerobic exercise program for sedentary older people improves cardiovascular function regardless of prior physical conditioning. The results of this study appear in the August 1 issue of Circulation.
"Older people have less reserve mechanisms to augment their heart function during physical activities than younger people do," said Edward Lakatta, M.D., Chief of the Laboratory of Cardiovascular Science at the NIA and the study's principal investigator. "But aerobic exercise conditioning can offset normal aging of the heart by making it a better pump, even for those who begin later in life, at age 60 or 70. In other words," points out Lakatta, "you don't lose the ability to get into condition. You can improve your heart's pump function, which declines with aging. But, the decline in maximum heart rate with aging is unaffected by conditioning," said Lakatta.
Lakatta and colleagues studied ten sedentary men and eight endurance-trained athletes, ages 58 to 62 years. All were healthy and free of heart disease. The sedentary, older men exercised for 24 to 32 weeks, and the athletes stopped their exercise for 12 weeks. Researchers measured the subjects' aerobic capacity and cardiovascular performance at the beginning and end of the study using a treadmill exercise test and a graded bicycle exercise test of the heart's ability to pump blood.
As a test of aerobic capacity, each man walked or ran to exhaustion on the exercise treadmill with a nose clamp and a tube in his mouth to measure oxygen intake and carbon dioxide output. This determined VO2 max, the maximum rate at which the body consumes oxygen during exhaustive exercise. VO2 max is determined by the heart's ability to pump blood through the lungs to pick up oxygen, deliver oxygen to working muscles, and have muscles extract oxygen from the blood. VO2 max reveals a person's level of aerobic capacity or fitness--the higher the better.
The men also had a state-of-the-art heart efficiency test. Each was injected with technetium, a radioisotope that adheres to red blood cells. A camera lens aimed at the person's chest while he pedaled on an exercise cycle photographed the radioisotope-labeled blood in the heart's left ventricle numerous times. A computer translated these measurements into an image of the pumping heart. Among other measures, the test determined the heart's ability to empty, which is an indicator of how strongly and efficiently the heart acts as a pump--another measure of cardiovascular fitness.
As the sedentary men trained and the endurance-trained athletes detrained, their cardiovascular performance, specifically their heart's ability to pump and their VO2 max, changed. With training, the sedentary men improved function and the athletes who stopped training lost function.
Prior to the study, the VO2 max averaged more than 55 percent higher in the endurance-trained athletes than in the sedentary men. The rise in the sedentary participant's VO2 max compared to the exercise trained participants' drop was about the same, with the rise being 11.3 percent (from 32.1 to 36.2 ml/kg/min) and the drop being 15.8 (from 49.9 to 42.0 ml/kg/min) with a margin of error of about 4.5 percent for each group. At peak effort on the exercise cycle, cardiac index, the amount of blood pumped each minute, improved from 8.5 to 9.3 l/min/m2 in the sedentary men as they exercised, and dropped from 10.5 to 9.4 1/min/m2 as the endurance-trained athletes stopped exercising.
Ejection fraction, the percentage of blood leaving the heart during each heart beat, changed in the sedentary men as they trained from 73 to 81 percent, and decreased, from 85.6 to 81 percent, in the endurance-trained athletes when they stopped exercising. The higher the ejection fraction, the better the heart's ability to pump oxygen-rich blood throughout the body. Ejection fraction improved as a result of the greater ability of the heart to squeeze down at the end of each heart beat. The latter increase was nearly twofold when compared over the extremes of the conditioning states.
"With age, the hearts of otherwise healthy sedentary people gradually lessen their ability to increase their heart rate and ejection fraction during acute exercise. Previous studies have shown that older people can benefit from aerobic exercise, but a novel aspect of this study found that the relative benefits were the same regardless of how fit they were when they started exercising," said Lakatta.
Age is a major risk factor for cardiovascular disease. The numbers of cases of heart disease and stroke rise steeply after age 65, accounting for more than 40 percent of all deaths among people age 65 to 74, and almost 60 percent at age 85 and above. For example, at maximum capacity, older athletes' heart function seems to be closer to that of younger men than to that of older men who do not exercise regularly.
Dr. Lakatta's colleagues include Jerome L. Fleg, MD and Frances C. O'Connor, MPH at the NIA, Gerontology Research Center; Jan Busby-Whitehead, MD, Andrew G.P. Goldberg, MD, and Loretta E. Lakatta, BSN at University of Maryland School of Medicine and Geriatrics Research, Education and Clinical Center, Veteran Administration Medical Center; James M. Hagberg, PhD at the Veterans Administration Medical Center, Divisions of Cardiology and Geriatrics; and Steven P. Schulman, MD, and Lewis C. Becker, MD at the Johns Hopkins Medical Institutions, Division of Cardiology.
The National Institute on Aging, part of the National Institutes of Health, leads the Federal effort supporting basic, clinical, epidemiological and behavioral research on aging and the special needs of older people.