Even If You Use It, You May Lose It!

Abstract & Commentary

By Ralph R. Hall, MD, FACP, ASM, Emeritus Professor of Medicine University of Missouri- Kansas City School of Medicine, Kansas City. Dr. Hall is a consultant for Aventis.

Synopsis: The decline in VO2 in healthy adults is not constant across age spans but accelerates markedly with each successive age decade despite increases in leisure time physical activity. The decline in aerobic capacity is greater in men than women.

Source: Fleg JL, et al. Accelerated longitudinal decline of aerobic capacity in healthy older adults.Circulation. 2005;112:674-682.

The ability of older persons to function independently is dependent on the maintenance of sufficient aerobic capacity and strength to perform daily activities. Peak aerobic capacity has been shown to decline with age. The rate of decline has previously been estimated from cross sectional studies. Cross sectional studies may provide an overly optimistic estimate of the changes that take place with age.

To determine the longitudinal rate of change in aerobic capacity and the influence of age, gender, and physical activity on these changes, Fleg et al performed serial measurements of peak treadmill oxygen consumption (peak VO2). The tests were performed in 375 women and 435 men ages 21 to 87 years of age who were enrolled in the Baltimore Longitudinal Study of Ageing, a community-dwelling cohort free of clinical heart disease, over a median follow-up period of 7-9 years.

A mixed effects regression model was used to calculate the change in peak VO2 expressed in ml per minute, for each age decade from the 20s through the 70s after adjustment for self-reported leisure time physical activity. A longitudinal decline in peak VO2was observed in each of the 6 age decades in both sexes. However, the rate of decline accelerated from 3-6% per 10 years in the 20s and 30s to > 20% per 10 years in the 70s and beyond. The rate of decline in the men was greater than in the women from the 40s onward. Similar rates of decline prevailed whether peak VO2 was indexed per kilogram of body weight or per kilogram of fat free mass, and in all quartiles of self reported physical activity. The longitudinal rate of heart rate decline averaged only 4% to 6% per 10 years and accelerated only minimally with age.

Fleg and colleagues concluded that the rate of decline in peak VO2 in healthy adults is not constant across age span but accelerates markedly with each age decade regardless of physical activity habits.

Commentary

There is both good news and bad news associated with this study. The bad news is that with ageing there is a continuing decline in aerobic fitness. The good news is that the more leisure time physical activity the better your aerobic fitness at all ages. These studies confirm the findings of Tanaka et al who found, in a cross sectional study, that the absolute but not he relative rate of decline was greater in highly active women (competitive runners) than that of sedentary women. In fact, many of the active women in their 60s and 70s had VO2 max levels similar to 20 and 30 year old sedentary women. The other good news, from a scientific point of view, is that this study provides an important data base from which a number of future studies can be done.

Fleg et al attempted to correct for fat free mass by calculating the ratio of the peak VO2 (mL/min) divided by the fat free mass. As Ades and Toth note, in their accompanying editorial,2 this may not be "a precise method for correction of fat free mass. However, it does make it unlikely that fat free mass accounts for the decline in aerobic fitness." Ades and Toth postulate that the delivery of oxygen to exercising muscle or the ability of muscle to use oxygen are more likely the determinants of declining aerobic activity.

There is still considerable controversy regarding the age related decline in peak VO2. Fleg and associates note there are prior studies in small homogenous samples in which middle aged and older men who continue to exercise vigorously experience significantly attenuated reductions in peak VO2.3 The work of Wang et al who followed runners over a 13-year period is also noteworthy. The runners not only had less reduction in their fitness and a longer life span but also a decrease in morbidity prior to death when compared to their sedentary controls.4

Recent physiological studies support the concept that endurance activity is an important factor in decreasing the decline in aerobic fitness. Eskurza et al5 found that brachial artery flow-mediated dilatation was 45% lower in sedentary older men than sedentary younger men but was preserved in endurance trained older men. Franzoni et al6 also noted that ageing is associated with oxidative stress and endothelial dysfunction. However, they also found that antioxidant activity and oxyradical scavenging was associated with preserved endothelial function in older endurance athletes. These positive changes may be associated with improved aerobic fitness and protection from adverse cardiac events.

Keep in mind that despite the more rapid decline in aerobic capacity with age, the level of fitness of the exercising individuals will be far better than those who are sedentary. The exercising group will likely have 5 or more years of life and be free of disabilities compared to their sedentary counterparts.

Encouraging people to exercise more is difficult. As we age we tend to give up endurance activities and many forms of exercise that are beneficial, such as yard work and heavy household chores.

We need to remember, however, that when you give up the hard things the easy things become hard.

References

1. Tanaka H, et al. Greater rate of decline in maximal aerobic capacity with age in physically active vs. sedentary healthy women. J Appl Physiol. 1997;83:1947-1953.

2. Ades PA, Toth MJ. Accelerated decline of aerobic fitness with healthy aging: what is the good news? Circulation. 2005;112: 624-626.

3. Kasch FW, et al. Ageing of the cardiovascular system during 33 years of aerobic exercise. Age Ageing. 1999;28:531-536.

4. Wang BW, et al. Postponed development of disability in elderly runners: a 13-year longitudinal study. Arch Intern Med. 2002;162:2285-2294.

5. Eskurza I, et al. Effect of acute and chronic ascorbic acid on flow-mediated dilatation with sedentary and physically active human ageing. J Physiol. 2004;556(Pt 1):315-324; Erratum in: J Physiol. 2004;556(Pt 3):1014.

6. Franzoni F, et al. Physical activity, plasma antioxidant capacity, and endothelium-dependent vasodilation in young and older men. Am J Hypertens. 2005;18:510-516.