Exercise and Longevity

Fran Finney

Who wants to grow old? If you are a regular Extropy reader, it is a fairly safe assumption that aging is not one of your favorite fantasies. Many of us have looked at length into various methods to slow down (ideally to stop) the aging process. A large number of these methods are experimental—some are quite expensive, some have no hard data to confirm that they actually do much good, and some even have mixed data suggesting that they could cause the opposite of what we wish to achieve. There is, however, one simple factor that we can add to our lifestyle that can be arbitrarily cheap, has little, if any risk of shortening our lifespan, and, increasing evidence shows that by making this simple factor a daily part of our lives, we can certainly retard some aspects of the aging process. That factor is regular physical stress to the cardiovascular and musculoskeletal systems, of long enough and intense enough duration to evoke a physiological response without causing irreparable damage, or, in a nutshell, exercise. This article is not meant to suggest that exercise alone should be considered as an adequate life extension regimen, but, added to other methods, it is certain to have positive effects.

A large number of physiological changes are associated with getting older. If we focus on physical deterioration we see decreases in athletic performance, caused by losses in:

• Muscle - Mass, strength, and performance speed;

• Aerobic capacity (V02max); and

• Joint flexibility;

And changes in body composition evidenced by:

• Decreased muscle mass;

• Decreased bone density; and

• Increased percent body fat

(see, e.g. [Cisar 91], [Crammer 87], [Pickles 83], [Shepard 90], [Shephard 91])

Although all of the above changes have been unequivocally associated with growing older, the causes are not clear.

Are these all normal developments within the aging process itself, or could they be caused by the decreased activity levels that usually accompany advancing age?

And, of course, there is the big question of life expectancy - not only do we want to remain as youthful as possible throughout our lives; we want to live longer as well! What effect, if any does exercise have on life expectancy?

Muscle Mass, Strength, and Performance Speed

Most people believe that the human body achieves its maximal muscular strength between the ages of 25 and 35 years. Although there is a great deal of variation in performance from person to person, typically, an individual’s strength declines at a steady rate after this age. In a sedentary adult, over time, muscular losses in mass, strength, and speed appear to be interrelated.[Costill 90A]

Let us first look at some of the physiological changes to muscle tissue that accompany aging. At birth, a person is born with essentially all the muscle fibers he/she will ever have. These muscle fibers increase in length as the child grows, and increase in cross-sectional area as demands are placed on them. (The cross-sectional area of a muscle is roughly proportional to its strength.) As a typical, sedentary adult ages, we see a decrease in the actual number of fibers in a muscle, a decrease in the size of the individual fibers, and a decrease in total muscle mass. The loss in number of fibers seems to be selective - most of the fibers that are lost are the fast-twitch, or type II fibers - fibers associated with quick bursts of strength and speed.[Costill 90A]

But, these changes are not universal. Barrie Pickles states in Biological Aspects of Aging:

“If skeletal muscles are used frequently, they show remarkably few structural and functional changes with age. The

majority of changes noted in the muscles of elderly persons are characteristics of disuse rather than age.”[Pickles 83]

Regular physical activity appears to minimize the mass and strength losses seen with aging A person who exercises regularly throughout his/her life may not show a significant decrease in either number or size of muscle fibers.[Costill 90A] Even the selective loss in fast-twitch fibers might not be necessary Costill speculates they are reabsorbed by the body in response to the inactivity observed with aging. Older adults who are physically active have been reported to have faster movement times than younger inactive adults.[Cisar 91]

How about a sedentary individual who becomes more active? Can such a person undo the effects of his/her previously inactive lifestyle? Once a muscle fiber has been lost, it cannot be replaced. However, individual muscle fibers can grow thicker. Furthermore, when type I fibers are subjected to chronic stimulation at a high frequency (i.e. speedwork) they alter their structure to resemble type II fibers. [Pickles 83]. So theoretically, a person should be able to replace bulk, strength, and speed in atrophied muscle. How does research bear this out?

Maria Fiatarone showed that significant gains in muscle strength could be shown in older adults who exhibited “atrophy of disuse”. Volunteers aged 86 to 96 participated in an 8-week exercise program consisting of three sessions per week of progressive-resistance exercises. Participant’s strength improved by an incredible average of 174%, muscle girth increased by 9% and speed improved by 48%.[Fiatarone 89,90] Other researchers have also reported marked improvements in muscular strength and mass.[Cisar 91] (Other cases of improvements in speed at which an activity is performed have also been reported, but it is not clear whether these improvements were due to true physiological changes, or whether they were due to a “practice effect”.)[Pickles 83]

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Aerobic Capacity (V02max)

V02max is considered to be the best measure of cardiovascular capacity, and is referred to by many sports medicine experts as the single most important indication of fitness level.[Shangold 88] It is defined as oxygen consumption at the point at which it fails to rise despite increasing exercise intensity. V02max is a function of the maximum rate that oxygen can be carried to and be utilized by body tissues.

An athlete has a much higher V02max than a sedentary individual. Average V02max in men declines with age almost 50%, from 48ml/kg-min at age 25 to 25.5ml/kg-min at age 75.[Costill 90B]

Two longitudinal (long-term) studies demonstrate how regular cardiovascular exercise as an individual ages can help prevent age-associated decrease in V02max. Fred Kasch demonstrated this in a study taking place over a span of 23 years. Thirty athletes were in the study - fifteen who had worked out regularly and vigorously over the entire period - and fifteen “controls” who had stopped training for at least 18 years. The average age at the start of the study was about 47, and at the end about 70. V02max declined 13% in the group that continued to exercise; in the de-trained group, the decline was 41%.[Kasch 90] A different study done by David Costill showed a 0.5% decline in V02max for competing track athletes (aged 50 to 82) over a period of 10 years, and a 14% decline in a similar group that stopped competing over the same 10 year period. [Costill 90B] According to Costill:

The decline in aerobic endurance seen throughout life appears to be affected more by the intensity and volume of regular exercise than by aging per se.

All of the groups in both longitudinal studies, even the active ones, did show at least a slight decrease in V02max. Most researchers attribute this to an age-related drop in maximum heart rate, or the fastest rate that an individual’s heart is physiologically capable of pumping at effectively. Can enough intense exercise prevent a drop in maximum heart rate? At this point the jury is out on this! At any rate, the slight drop in V02max noted in the competing track athletes in Costill’s study was not functionally significant.

Cross-sectional studies (comparing different groups) also show that exercise does affect cardiovascular capacity. Endurance athletes consistently have higher V02max values than sedentary individuals of the same age.[Kavanagh 90], [Cisar

91], [Shephard 91].

Joint Flexibility

To understand changes in joint flexibility that accompany aging, first we need to look at the connective tissue that holds joints together and provides cushioning and lubrication for the joints. All connective tissue cells contain a variety of substances, including: collagen, which provides structure and tensile strength; elastin, which provides elastic flexibility; glycoproteins that enable tissue to retain fluid and stay well-hydrated; and hyaluronic acid, to provide lubrication. As a healthy, active adult ages, dynamic collagen production continues, in response to stresses placed on the body. However, production of elastin, some glycoproteins, and hyaluronic acid diminishes. Clinically, we see the following:

1. The diameter of collagen fibers in a given location of the body increases. This increases the tensile strength of the connective tissue, but reduces its elasticity.
2. The amount of elastin in the skin, bronchial tree, and large arteries is reduced; the elastic properties of these areas are therefore reduced.
3. Lowered production of fluid-holding glycoproteins causes progressive tissue dehydration.
4. Reduced hyaluronic acid secretion causes increased joint friction.

To make matters worse, elastin is not produced at all in an older adult, so when a person’s elastic connective tissue is injured, the tissue is replaced with inelastic, collagenous based connective tissue. Cartilage (which provides cushioning and some stability to the joints) also cannot be replaced. Therefore, as a person ages, cartilage is worn away.[Pickles 83] All of the above changes can decrease flexibility and make movement more difficult. Exercise, while it does not seem to alter these physiological changes, can make degenerative changes in the joint functionally less restrictive. Although damaged cartilage can not be replaced, regular non-stressful exercise has been shown to reduce degeneration in articular cartilage. [Pickles 83] True elasticity in the joints does diminish, but functional flexibility as demonstrated by range of motion can be maintained through a program of stretching. [Cramer 87], [Cisar 91]. And increased joint activity, although it does not cause production of elastin, will increase the tensile strength of the ligaments holding the joints together, by increasing the col

lagen production - which will strengthen the joints and make them more resistant to injury.

Changes in Body Composition

Three measurable structural components of the human body are muscle, bone and fat. [Shangold 88] In the general population, with increasing age, we see a decrease in muscle mass, a decrease in bone density, and an increase in adipose tissue (fat.) Regular exercise can prevent loss of muscle mass as a person ages, and can also increase muscle mass in older individuals. Let us now look at how exercise can affect bone density and percent body fat as a person ages.

Bone Density

Although people tend to view bone as an inert substance, it is actually a very active tissue. Bone is constantly being remodeled, in response to stresses and forces placed on it. Assuming an adequate diet and no hormonal abnormalities, the stronger the force applied to a section of bone tissue, the stronger that section of bone will become. Likewise, when less force is applied to a section of bone, excess material is reabsorbed by the body, and the bone becomes lighter and more fragile.

Bone mineral content starts to decline at about age 40 to 50 years, with a subsequent loss of about 10 percent per decade. It is possible that (aside from the bone loss associated with decreased estrogen in women at menopause) the smaller amount of bone in the elderly could be entirely caused by an age-associated decrease in activity.[Pickles 83] Less activity leads to a reduction in the stresses and strains placed on the bone, which triggers the body’s reabsorption mechanisms.

It appears that both weight bearing and muscle action are important in the maintenance of normal bone density. Studies where weight bearing alone (in paralyzed patients) or muscle movement alone (in astronauts) were attempted to reduce bone loss, showed that either by themselves was not very effective. However, combining compression of a bone with the simultaneous activity of its overlying muscles (i.e. weight bearing exercise) does produce increased density and cortical thickening of the bone.[Pickles 83]

Leslie Pruitt worked with post-menopausal women to see how a weight training program would affect their bone mineral content. At the end of nine months the bone mineral content in their spines had increased, while it decreased in a control group of women who did not

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EXTROPY #9 Summer 1992

exercise.[Pruitt 90] Other researchers show similar results in both sexes.[Cisar 91], [Crammer 87], [Shephard 91]

Body Fat

Numerous studies have shown that regular aerobic exercise can effectively maintain or reduce percent body fat.[Cisar 91], [Kasch 90], [Shangold 88], [Shephard 91] In a 23 year longitudinal study discussed earlier in this paper, lead by Frank Kasch, the exercising group lost an average of 7.5 pounds, compared with their individual weights taken at the start of the study. The nonexercising group, in contrast, gained an average of 6.8 pounds. Percent body fat was not taken at the start of the study. But at age 70, the exercisers averaged 15.9% body fat and the nonexercisers averaged 25.7%.[Kasch 90]

Cross-sectional studies demonstrate the same effect. For example, female distance runners in their 30’s average about 15% body fat, while a sedentary 30-year-old woman averages 27%. [Shangold 88]

How effective is exercise as a mechanism for losing body fat? Can a previously sedentary, obese individual lose excess body fat through increased activity? The American College of Sports Medicine has concluded that to lose a significant amount of body fat (greater than 5%) through exercise alone, an individual must exercise at least 20 minutes per day, 3 days a week, at a sufficient intensity and duration to burn 300kcal per session. Combining increased exercise with a modest reduction in calories can be much more effective in reducing percent body fat. However, reduction of calories accompanied by a reduction in physical activity results in a higher percent body fat - most of the weight loss being due to loss of muscle tissue and fluids.[Shangold 88]

Human Growth Hormone and its Relationship to Exercise and Aging

It has been suggested that the changes in body composition associated with aging are due at least in part to a decreased secretion of human growth hormone (GH). Secretion of human growth hormone generally decreases with age after the third decade of life.[Rudman 90], [Lancet ed. 91] Decrease in lean body mass, and increase in adipose tissue have been correlated with decreased levels of this hormone; these changes in body composition can be reversed by replacement doses of the hormone. [Rudman 90] Increased GH levels have also been associated with fewer by-products of tissue breakdown after intense exercise and decreased

muscle soreness.[Elam 89] Administration of growth hormone by injection three times a week to GH-deficient men over sixty was shown over a six month period to significantly increase lean body mass, decrease percent body fat, increase skin thickness, and increase lumbar vertebral bone density.[Rudman 90] However, currently such administration, besides costing $14,000 a year [Smith 90] is not available to the general Extropian. In addition, there are potential health complications. Short-term side-effects of existing GH-replacement on GH-deficient adults include edema, arthralgia, hypertension, and carpal tunnel syndrome.[Lancet ed. 91] There is also an increased risk of cancer in acromegalic adults - adults with abnormally high secretion of GH. (Unfortunately, cancer cells seem to respond to growth factors as well as normal cells.) This has not been ruled out as a serious possible complication of long-term high-level GH therapy.

It has been suggested that the anti-aging effects of exercise could be due to increased secretion of GH. Studies have shown a pronounced increase in levels of human growth hormone immediately following exercise - both in men in their 20’s, who went from a pre-exercise average level of 2.5 mcg/l to a post-exercise average level of 12.5 mcg/l[Quirion 88] and in men over 50 (pre-exercise .8 mcg/l; post exercise 9.3 mcg/l, and one hour later 3.7 mcg/l). [Metivier 88] The documented effects of exercise alone, as compared to growth hormone administration alone, show similar effects on body composition and muscle strength. Exercise studies have been able to demonstrate greater gains in less time - perhaps since there is not as much need to be concerned with potential complications in moderating “dosage” level! Also, so far studies on growth hormone have not shown any effect on functional flexibility, aerobic capacity, or muscle performance speed.

There is some indication that diet can affect physiological secretion of growth hormone in response to exercise. Men on very high carbohydrate, hyperinsulin-inducing diets (diets that cause high levels of insulin to be present in the blood) did not increase their GH levels after exercising as much as men on low-carbohydrate diets with associated low insulin blood levels, although GH levels still increased significantly.[Quirion 88] There are serious problems associated with being in a perpetually hypoinsulemic (low insulin) state, and with the excess of fat and protein that accompany a low carbohydrate diet. However, a much safer and effective alternative is available. Supplementing otherwise unaltered diets with the

amino acids L-arginine and L-ornithine shortly before exercise and before bed (nominal times for increased GH secretion) showed significant evidence of increased growth hormone secretion - and a more pronounced increase in muscle mass and strength and decreased tissue breakdown by-products than exercising, placebo-supplemented controls.[Elam 89] Combining exercise, a healthy diet, and amino acid supplementation would show all the benefits of an exercise program, with perhaps an increased effect on increased muscle mass and strength, decreased adipose tissue, and decreased muscle soreness as a result of enhanced GH release in response to exercise.

Other Age-Related Traits

Besides purely athletic deterioration, we see many serious health problems associated with aging. Of these age-related problems, several can be reduced and controlled through a regular program of exercise. Exercise alone has been shown to have protective effects against high blood pressure[Kasch 90], [Tanji 90], coronary heart disease[Shephard 91], [Omish 90], stroke[Blair 89], and non-insulin dependent diabetes[Staten 91].

As an individual ages, his/her proprioceptive senses become less accurate, causing losses in balance and coordination. Although the mechanisms for these losses are poorly understood at this time [Pickles 83], research has shown that decreases in balance and coordination are reduced by regular exercise. [Cramer 87], [Cisar 91]

People also associate general decreases in mental functions and reaction time with aging. Robert Dustman showed that sedentary adults ages 55 to 70 who were put on a “vigorous” exercise program showed significant improvement in response time, memory, and mental “flexibility”, when compared with a control group that was not put on the exercise program.[Dustman 91]

And what about lifespan? Regular exercise apparently can help us function at a “younger” level, but can it prolong life? Research indicates that it can. In one study, involving 16,000 men, those who walked 9 or more miles a week had a lower mortality rate than those who walked less than 3 miles. [Dustman 91] Another study involved comparing mortality rates of 13,000 men and women at different fitness levels. Fitness was categorized according to V02max - and subjects were grouped into five categories. After adjusting for age differences, smoking, and cholesterol, the subjects in the least-fit category still had death rates 3.4 times higher

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for men, and 4.6 times higher for women than subjects in the most-fit category.[Blair 90]

It might seem from some of the information presented in this paper that we have found a virtual panacea to keep our bodies from aging physically: muscle strength, speed, and mass can be maintained; bone mass need not decrease; percent body fat can be kept at a youthfully low level; aerobic capacity can for the most part be maintained - and losses in flexibility, coordination and balance can be minimized. However, exercise alone cannot stop some aspects of aging: As a person ages, his immune system deteriorates, making him more susceptible to disease and its associated periods of inactivity. Injuries take longer to heal. Cartilage breaks down and is not replaced. This, combined with the typical age-related decrease in secretion of hyaluronic acid, causes progressive osteoarthritis in the joints, which also makes adherence to an exercise schedule more difficult. Barrie Pickles states in Biological Aspects of Aging:

The key to preventing the normal age-related changes from affecting functional capacity for ease of movement during the entire lifespan is a gradually increasing adherence to a

program of physical fitness. As a person ages, physical fitness becomes more and more important. [Pickles 83]

As a person ages, physical fitness also becomes more and more difficult to maintain - requiring greater determination and willpower. But the rewards - enjoying a functionally more youthful, productive, and potentially longer life, are certainly worth the extra effort!

REFERENCES

Blair, S.: Exercise Can Enable You to Live Longer. Randal Wellness Newsletter 1990; 2(1):1

Blair, S.: Low Fitness May Mean Higher Risk of Stroke. The Physician and Sportsmedicine 1989;17(9):37-4

Cisar C.J., Kravitz, L.: Turning Back Time: Exercise and Aging. Idea Today 1991; 9(1):28-36

Costill D.L.: Muscular Strength and Aging. Sports Medicine Digest 1990A; 12(8):4

Costill D.L.: Endurance Performance and Aging. Sports Medicine Digest 1990B; 12(10): 7

Crammer E., Mummert C.: Reach Out To Seniors. Dance Exercise Today 1987; 5(10):5-8

Dustman R.: Successful Aging. University of California at Berkeley Wellness Letter 1991; 7(11):1

Elam R.P., Hardin D.H., Sutton R.A.L., Hagen L.: Effects of Arginine and Ornithine on Strength,

Lean Body Mass, and Urinary Hydroxyproline in Adult Males. The Journal of Sports Medicine and Physical Fitness 1989; 29(1): 52-56

Fiatarone M.A.: Strength Improvements at any Age. Running & FitNews, American Running and Fitness Association 1989; 7(11): 1

Fiatarone M.A., Marks E.C., Ryan N.D.: High-intensity Strength Training in Nonagenarians: Effects on Skeletal Muscle. Journal of the American Medical Association 1990; 263(22):3029-3034

Kasch F.W., Boyer J.L., Van Camp, S.P., et al: The Effect of Physical Activity and Inactivity on Aerobic Power in Older Men (A Longitudinal Study). The Physician and Sportsmedicine 1990; 18(4):73-83

Kavanagh T., Shephard R.J.: Can Regular Sports Participation Slow the Aging Process? Data on Masters Athletes. The Physician and Sportsmedicine 1990;18(6):94-104

Lancet Editorial: Growth Hormone Therapy in Elderly People. The Lancet 1991;3B7:1131-1132

Metevier G., Gauthier R.: The Effects of Acute Physical Exercise on Blood Serum Cholesterol, Triglycerides, Human Growth Hormone (HGH) and Free Thyroxine (T4) in Men over Fifty Years of Age. The Journal of Sports Medicine and Physical Fitness 1988; 28(1):7-10

Omish D., Brown, S.E., Scherwitz, L.W. et al: Can Lifestyle changes reverse coronary heart disease? The Lifestyle Heart Trial. Lancet 1990; 336:129-133

Pickles B.: Biological Aspects of Aging. Physical Therapy of the Geriatric Patient 1983; (edited by Osa Jackson):27-63

Pruitt L.: New Findings To Keep Bones Strong. Running & FitNews, American Running and Fitness Association 1990; 8(9):4-5

Quirion, A., Brisson, G., De Carufel, D., et al: Influence of Exercise and Dietary Modifications on Plasma Human Growth Hormone, Insulin and FFA. The Journal of Sports Medicine and Physical Fitness 1988; 28(4):352-353

Rudman, D., Feller, A.G., Nagraj, H., et al: Effects of Human Growth Hormone in Men Over 60 Years Old. The New England Journal of Medicine 1990; 323(1):1-6

Shangold, M.M., Mirkin, G.: Women and Exercise; Physiology and Sports Medicine. 1988 Philadelphia: FA Davis Co.

Shepard, J.G., Pacelli, L.C.: Why Your Patients Shouldn’t Take Aging Sitting Down. The Physician and Sportsmedicine 1990; 18(11):83-90

Shephard, R.J.: Exercise and Aging. Mayo Clinic Health Letter, special supplement, June 1991

Smith, J.A., Wiedemann, M.J.: referenced letter to the editor: The New England Journal of Medicine, 1990;323(22): 1562

Staten, M.A.: Managing Diabetes in Older Adults - How Exercise Can Help. The Physician and Sportsmedicine 1991; 19(3) 66-79

Tanji, J.L.: Hypertension - Pt 1: How Exercise Helps. The Physician and Sportsmedicine 1990; 18(7)77-82

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EXTROPY #9 Summer 1992