The physiology of aging as it relates to sports

The physiology of aging as it relates to sports

Edward H. Nessel

All graphs, charts and tables were reproduced with permission from The McGraw-Hill Companies and excerpted from Jack H. Wilmore and David L. Costill, Physiology of Sport and Exercise, 2nd edition, 1999, McGraw-Hill.

Overview

Athletes today of all ages and abilities are on a quest for optimum performance and in that quest, age often becomes secondary. Opportunities are more evident now than ever before for older athletes to compete in various sports activities, both within an age bracket and in open competition. But even the most highly-trained older person experiences a decline in performance after the fourth or fifth decade of life (1).

We can readily agree that repeated vigorous activity is extremely important to maintaining robust health into advanced age; however, there are differences in physiologic parameters that occur with the aging process. Even at a high level of condition, the older athlete simply requires more recovery time than a younger athlete to engage in a repeat maximum effort.

Of course, there is another vital variable that should be addressed regarding one’s overall potential. That element is simple genetics. “Picking the right parents” and being the recipient of a great mix of DNA can influence up to 50% of an athlete’s ability to perform at a superior level (2). But how much of that ability is maintained throughout the years directly varies according to how much vigorous exercise is performed during later years in life.

[FIGURE A OMITTED]

The following parameters will be discussed and illustrated: sports performance comparisons by age; respiratory, cardiovascular, strength and body composition changes with aging; trainability of the older athlete and how training can delay decline in exercise performance.

Sports Performance

Records in running, swimming, cycling and weight lifting suggest that our physical prime comes during our 20s or early 30s. Although older runners have achieved exceptional records, running performance generally declines with age and the rate of this decline appears to be independent of distance. Longitudinal studies of elite distance runners indicate that despite a high level of training, performance in events from the mile to the marathon declines at a rate of about 1% per year from the age of 27 to 47 years (3, 4). In a cross-sectional analysis, American records for both the 100m and 10km runs also decrease by about 1% per year from age 25 to 60. Beyond age 60, however, the records for men slow by nearly 2% per year. Another cross-sectional sprint-running test of 560 women between the ages of 30 and 70 revealed a steady decline in running velocity of 8.5% per decade (0.85% per year). The patterns of change are about the same in both sprint and endurance running performances (see Figure A).

A study of past national Masters swimming championships (1991-1995) shows that for the 1500m freestyle, both men and women slowed steadily from age 35 to about 70. After age 70, swimming times slowed at even a faster rate. Furthermore, the rate and magnitude of the declines in both the 50m and 1500m freestyles were greater for females than males (5). Another analysis (see Figure B) shows a comparison of U.S. Masters swimming records in the 100m freestyle; the times get slower by about 1% per year for both men and women from age 25 to age 75. Interestingly, though, because success in this sport depends on skill as well as on strength and endurance, some U.S. Masters swimmers have reached their personal best performances from ages 45 to 50.

Optimal cycling performances are typically seen between the ages of 25 to 35. Male and female cyclists’ records (for the 40km) drop at about the same rate with age–an average of 20 seconds (0.6%) per year. The U.S. national cycling records for the 20km distance demonstrate a similar pattern for both sexes. For this distance, speed decreases by about 12 seconds (0.7%) per year from age 20 to nearly age 65 (6).

In general, maximal muscle strength peaks between the ages of 25 and 35. Beyond that age range, the ability to lift weight declines at a steady rate of about 1.8% per year. Of course, as with other measurements of human performance, individual strength varies considerably.

What then are the specific parameters which cause inevitable declines in athletic performance?

Changes in Cardiorespiratory Endurance with Aging

To a large extent, changes in endurance performance that accompany aging are caused by decrements in both central and peripheral circulation. Measurements of cardiac output and limb blood flow are not easily performed and, therefore, early studies of the effects of aging on the physiology of endurance exercise examined maximum oxygen uptake (VO2max). This is a parameter that closely parallels maximal cardiac output (see Table 1). More recently there have been efforts to measure blood flow and oxygen exchange in the leg muscles of exercising older subjects; however, these studies are limited in number.

[FIGURE B OMITTED]

Studies of Normally Active People

The first critical studies of the aging process and physical fitness were done in the late 1930s (8). It was learned from these studies that VO2max in normally active men declined steadily from age 25 to age 75 at about an average of 1% per year (see Table 2). This is the same rate of decline seen in endurance running, swimming and cycling performances. More recently, a review of 11 cross-sectional studies, most involving men under age 70, examined the rate of decline in VO2max with age; these showed a decrease of from 0.8% to 1.1% per year (9).

In the few longitudinal studies performed in this area (10, 11, 12), a wide range of decline in aerobic capacity was seen, but these variations can be attributed to the subjects’ different activity levels and ages at the beginning of the studies. Nevertheless, the rate of decline in VO2max is generally agreed to be approximately 10% per decade or 1% (0.4ml/kg. min.) per year in relatively sedentary men. Some studies have shown that, on average, women demonstrate a lower rate of VO2max decline with age (0.2 to 0.5ml/kg min.) per year than men (8). Others show no difference (13, 14).

To provide a more accurate comparison of VO2max values in men and women and changes in aerobic capacity with aging, one should use actual readings of liters/min of oxygen uptake rather than the relative reading with the increased body weight component. Comparisons of such aerobic capacity values do not take into consideration the individual’s initial VO2max values. For example, a decline of 0.5ml/kg X min in someone with an initial value of 30 ml/kg X min would have a greater impact than in someone with a value of 50ml/kg X min. It makes more sense to compare groups of people in terms of their percentage change in VO2max, which can be calculated as follows: % change = VO2max-initial VO2max / initial VO2max.

Using this formula, it has been shown that both men and women lose about 1% per year in aerobic capacity. This decline is caused primarily by a reduction in maximum heart rate and stroke volume and, in turn, decreased cardiac output.

Studies of Older Athletes

Researchers at the Harvard Fatigue Laboratory looked at former elite runners for a span of 30 years. Results showed that runners who did not continue to train during middle age showed much larger declines in aerobic capacity (43% decline on average from age 23 to 53) than those who “stayed in shape” (15). These facts seem to prove that prior training offers little advantage to endurance capacity in later life, unless a person continues to engage in some form of vigorous activity (see Figure C).

Another study observed that, over a 10-year period, track athletes (ages 50 to 82) who continued to train and compete were able to maintain their VO2max values at a fairly high level. But those who reduced their training showed a significant decline in aerobic capacity (16). Other changes, however, were the same for both groups: (a) maximum heart rate decreased by about 5 to 7 beats/min per decade, (b) body weight increased from an average of 154 lbs to 164 lbs, and (c) body fat increased significantly from about 13% to over 18%.

More recent longitudinal studies of older runners and rowers have reported a decline in aerobic capacity, cardiovascular function and changes in muscle fiber composition with aging (17, 18, 19, 20). These athletes were studied for as long as 28 years and in that time, some continued to train for competition while others became quite sedentary. Those athletes who trained hard experienced a 5% to 6% decline in VO2max per decade. Those who stopped training experienced nearly a 15% decline in aerobic capacity per decade.

[FIGURE C OMITTED]

It is now commonly accepted that reducing the effects of aging (on endurance) depends a great deal on the individual’s training adaptability. It also appears that high intensity training has a slowing effect on the rate of loss in aerobic capacity during the early and middle years of adult life (30 to 50 years of age), but less effect after age 50.

Respiratory Changes with Aging

It appears that age-related loss of lung tissue elasticity and attendant stiffening of the chest wall are the prime factors in reduced respiratory capacity (universally occurring in sedentary individuals). Declines occur in both the vital capacity (total volume of air expelled after maximal inhalation) and forced expiratory volume in one second (the greatest volume of air exhaled in one second). These declines occur linearly with age, starting between ages 20 to 30, while residual volume (the amount that cannot be exhaled) increases and the total lung capacity remains unchanged. As a result, the ratio of the residual volume (RV) to the total lung capacity (TLC) increases and less air can be exchanged. In our early 20s, RV accounts for 18% to 22% of the TLC, but this increases to 30% or more as we approach age 50.

These changes are matched by changes in maximal ventilatory capacity during exhaustive exercise. Maximal expiratory ventilation (VEmax) increases until physical maturity and then decreases with age. VEmax values average about 40 L/min for 4 to 6 year old boys, increase to 110 to 140 L/min for fully mature men and then decrease to 60 to 80 L/min for 60 to 70 year old men. Females follow the same general pattern, although their absolute values are considerably lower at each age, primarily because of smaller stature.

During middle and older age, endurance training decreases the loss of elasticity from the lungs and chest wall. As a result, endurance-trained older athletes have only slightly decreased pulmonary ventilation capacities. Decreased aerobic capacity among these older athletes cannot be attributed to changes in external respiration. Also, during strenuous exercise, both normally active older people and athletes can reach nearly maximal arterial oxygen saturation (97%) (21). Therefore, neither changes in the lungs nor in the blood’s oxygen-carrying capacity appear to be responsible for the observed drop in VO2max reported in aging athletes. Rather, the primary limitation is apparently linked to oxygen transport to the muscles.

Cardiovascular Changes with Aging

Cardiovascular function also diminishes as we age. One of the most notable changes is a decrease in maximum heart rate (HRmax). Whereas children’s values frequently exceed 200 beats/min, the average 60-year-old has an HRmax of approximately 160 beats/min.

The reduction in HRmax with age is similar in both sedentary and highly trained adults. At age 50, for example, normally active men have the same HRmax values as former and still-active same aged distance runners. This reduction in HRmax might be due to morphological and electrophysiological alterations in the cardiac conduction system, specifically in the sino-atrial (SA) node and in the bundle of Hiss slowing cardiac conduction (22). Also, the heart becomes less sensitive to the body’s chemical catecholamine stimulation.

[FIGURE D OMITTED]

Another parameter negatively influencing aerobic capacity is the decrease in stroke volume (SVmax); the culprit here becomes increased total peripheral resistance from reduced pliability in the arteries and possible reductions in left ventricular contractility.

The decrease in VO2max with aging and inactivity then is largely explained by decreases in cardiac output (CH = heart rate x stroke volume), along with the body’s lessened ability to extract oxygen from the blood supply.

When compared to sedentary men of the same age, those who were consistently active had higher VO2max values because of greater stroke volumes and greater maximal cardiac outputs; however, an older athlete will still have less of all three important cardiac output functions than the younger athlete (see Figure D).

The combination of increased peripheral vascular resistance (see Figure E), increased body weight and age-related changes in the respiratory and cardiovascular systems cause a decreased VO2max in men by about 10% per decade after age 25. But if the body composition and physical activity are kept constant, deterioration due to the aging process results in a VO2max decline of only about 5% per decade (see Table 1).

Some research indicates that older athletes who train with the same intensity and volume as their younger counterparts can have as little as a 1% to 2% decrease in aerobic capacity per decade until age 50; after age 55, a more marked reduction in cardiovascular capacity will occur.

Changes in Strength with Aging

Maximal strength decreases steadily with aging. In sedentary individuals, the ability to stand from a sitting position is compromised at age 50 and by age 80, becomes impossible for some. Another daily task of living, opening a jar set at a specific resistance, can be performed by 92% of men and women in the age range of 40 to 60 but after age 60, the failure rate becomes 68%. By ages 71 to 80, only 32% can open the jar (21).

Similar data describe leg strength changes with aging in men. Knee extension strength in normally active men and women decreases rapidly after ages 45 to 50, but strength-training the knee extensor muscles enables older men to perform better at age 60 than most normally active men at half that age.

[FIGURE E OMITTED]

Many studies covering a period of over 20 years conclude that the amount or intensity of activity, or perhaps both, might play an important role in fiber-type distribution (23, 24). The apparent increase in slow-twitch (ST) muscle fibers with aging and/or disuse is due to the decrease in the number of fast-twitch (FT). Though the precise cause of this is unclear, it has been suggested that the number of FT motor neurons decreases and thus, innervation of the muscle fibers is halted. Additionally, the maximum discharge rate of the motor-neuron unit is distinguishably less than with the young. This causes strength reduction due to an impaired ability to fully drive the existing motor units (25). Research also indicates that approximately 10% of the total number of muscle fibers is lost per decade after age 50 which may explain, in part, age-related muscle atrophy (26).

The good news is that strength training can preserve, even enhance, the cross-sectional area of the trained muscles no matter what the age. Aging appears neither to impair the ability to improve muscle strength nor to prevent muscle hypertrophy (larger mass).

Body Composition and Aging

Although we see that athletes of any age are leaner than their less active counterparts, older athletes, for the most part, have substantially more body fat than younger athletes.

Beyond age 30, the body has a normally reduced ability to mobilize fat. This, coupled with gradual decrease in lean-body mass from lessened physical activity, allows for an increased percentage of total body fat. As one might suspect, the body fat content of physically active people is significantly lower than that of age-matched sedentary people. Highly trained male and female runners at an average age of 45 years, for example, have been reported to average 11% and 18% body fat, respectively. This is considerably lower than percentages reported for sedentary people of similar age: 19% in men and 26% in women.

Older competitive swimmers (average age 50 for men and 43 for women) have less body fat than age-matched sedentary people, yet these athletes are fatter on the average than a group of equally fit distance runners; the male and female swimmers average 15% and 23% body fat, respectively. This, of course, is partially due to the gravity-free environment of water and the supine position of the body while swimming. Both allow the body to exercise vigorously while maintaining a lower heart rate and thus, lower caloric expenditure.

Trainability of the Older Athlete

Despite decrements associated with aging, older athletes are capable of exceptional performances. Their ability to adapt to endurance and strength training is well-documented. Studies have shown that improvements in VO2max with training are similar for younger (ages 21 to 25) and older (ages 60 to 71) men and women (27, 28). While the baseline readings for VO2max were lower for the older athletes, the absolute increases with training were similar. This can be explained by the fact that older individuals show greater improvement in the muscles’ oxidative enzyme activities. Improvement in younger persons is largely due to increased maximal cardiac output.

In summary, review of scientific literature has shown that although we cannot halt “Father Time” and his inexorable march toward our decline with aging, we can fight back to a large extent by taking up the cause of regular endurance training, strength training and good nutritional habits.

Youth may be wasted on the young, but a wise person of years need not be envious. He can make the best of his existence and enjoy a healthy and vigorous life (29).

Table 1 Changes in Aerobic Capacity and Maximal Heart Rates With Aging

in a Group of 10 Highly Trained Masters Distance Runners

[dot.V][O.sub.2]max

Age (years) Weight (kg) (L/min)

21.3 ([+ or -]1.6) 63.9 ([+ or -]2.2) 4.41 ([+ or -].09)

46.3 ([+ or -]1.3) 66.0 ([+ or -]0.6) 4.25 ([+ or -].05)

(ml * [kg.sup.-1] * [min.sup.-1]) HRmax (beats/min)

69.0 ([+ or -]1.4) 189 ([+ or -]6)

64.3 ([+ or -]0.8) 180 ([+ or -]6)

Note. Values are [+ or -] SE.

Table 2 Changes in [dot.V][O.sub.2]max Among Normally Active Men

Age [dot.V][O.sub.2]max % change from

(years) (ml * [kg.sup.-1] * [min.sup.-1]) 25 years

25 47.7 —

35 43.1 -9.6

45 39.5 -17.2

52 38.4 -19.5

63 34.5 -27.7

75 25.5 -46.5

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by Edward H. Nessel, R.Ph., M.S., M.P.H.

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