"Older subjects are less efficient than younger subjects. This inefficiency can be reversed by aerobic exercise training," said Wayne C. Levy, M.D., F.A.C.C. from the University of Washington in Seattle.
"It is well known that aging is associated with reduced exercise capacity. What is less appreciated is that older subjects have an additional impairment in exercise capacity due to exercise inefficiency. For example, the older subjects used about 20 percent more oxygen to walk at 3.5 miles an hour than the younger subjects. Thus, the older subject walking at 3 miles per hour and the younger subject walking at 3.5 miles per hour used the same amount of oxygen. With training, this disparity with aging was abolished," he added.
The researchers from the University of Washington and the Veterans Affairs Puget Sound Health Care System in Seattle, including lead author J. Susie Woo, M.D., compared participants in their 20s to early 30s (15 women and 12 men) to those in their mid-60s to late 70s (16 women and 18 men).
Before training, the younger participants had a much higher exercise capacity, as shown by a peak oxygen consumption (delivery of oxygen to exercising muscle) that was 42 percent higher. Younger participants also didn't have to work as hard and were 8 percent more efficient than the older participants.
Then all the participants were entered into a supervised aerobic exercise program. Three times per week they walked or jogged, bicycled, and stretched, doing each for 30 minutes during a 90-minute workout session.
After three to six months, the older subjects on average boosted their peak work output by 29 percent, due to increased oxygen delivery and exercise efficiency. While the older subjects were 30 percent more efficient at exercising than they were before training, the younger subjects improved only 2 percent.
Training did benefit the younger subjects, too, but rather than becoming more efficient, the younger participants boosted their peak oxygen consumption.
The authors wrote that since the older participants were able to erase many of the starting differences in exercise factors, some of the decline typically seen with aging may not be inevitable; rather it may reflect a lack of fitness, which can be addressed with training.
Dr. Levy said their results leave some question unanswered.
"It is unknown the duration, intensity, and mode of exercise training necessary to improve efficiency in the older subjects. Will simple walking for two to four weeks be adequate or is more vigorous exercise necessary?" he noted.
"What was new and unexpected in our study was the disproportionately greater response to training in the elderly subjects," the authors wrote.
Edward G. Lakatta, M.D., from the National Institute on Aging Intramural Research Program, Gerontology Research Center in Baltimore, Maryland, who wrote an editorial in the journal with Paul D. Chantler, Ph.D., pointed out that this study looked at oxygen consumption and exercise efficiency in a way most studies have not. The results offered both good and bad news about aging.
"In summary, the bad news conveyed to us by Woo et al. is that metabolic debts associated with the performance of dynamic exercise increase with aging. These debts, paid during recovery from exercise are likely attributable to an inability of the older body to adapt to the energy requirements of exercise," they wrote.
But there was also good news in the results.
"A relatively low level of aerobic training for six months was able to improve exercise efficiency, reduce oxygen debt and an increased exercise capacity in older men and women. In addition after training the older individuals showed a lower oxygen debt, lower oxygen consumption during recovery, and better exercise efficiency than the untrained young individuals!" Dr. Lakatta said.
Joseph A. Franciosa, M.D., a pharmaceutical industry consultant who was not connected with this study, said it is a very well done study comparing exercise capacity and exercise efficiency in healthy subjects.
"Since these are otherwise healthy subjects, this age-related difference probably reflects a degree of physical deconditioning as people become less physically active with aging. The same thing is observed in a number of disease states and it is unclear if these changes are due to something specific to the underlying disease or if they simply reflect deconditioning due to reduced physical activity imposed by the disease," Dr. Franciosa said.
He said the improvement seen in older subjects after exercising is important.
"The practical significance of this is that elderly people should not be afraid to exercise, which is good for them. If they are otherwise in good health, they should remain physically active and not "slow down" just because of age. If they have medical problems, exercise can still be of considerable value, but this should be undertaken only under a physician's supervision," he said.
Bernard Chaitman, M.D., F.A.C.C., from the St. Louis University School of Medicine, who also was not connected with this study, said the results and the way the study was done help shed light on how training benefits older people.
"Although the study design was cross-sectional, and did not contain middle-aged or very elderly subjects, the data clearly show that improved oxygen efficiency contributes to the improvement in exercise capacity after training in older subjects. Physicians should encourage their older patients to exercise on a regular basis to improve quality of life and functional performance," Dr. Chaitman said.
Journal
Journal of the American College of Cardiology