Your Fitness Age is the One that Really Counts

by Susan Krauss Whitbourne, Ph.D.

Age may be just a number, but it’s one you can change

fitness ageMany people would agree that we benefit from the increased experience that getting older brings. However, with each passing year, the aging of the body creates its own difficulties in everyday life. There are the inevitable aches, strains, and pains of our aging bones, joints, and muscles not to mention changes in appearance that make it more difficult to feel accepted in a youth-oriented society.

The one truth about aging is that it’s intimately linked with the passage of time. We may be able to alter the clock by setting it forward or backward an hour depending on the season, but we can’t set it back for more than that, much less days, months, or years. No one has figured out how to alter the body’s pace-setter cells that mysteriously link the body’s aging with the number of times the earth revolves around the sun.

Just as the average person may bemoan the basic fact that aging and time are completely tied together, scientists who study the aging process find their job made far more difficult by this age-time conundrum. Are the changes we think due to aging actually due to social and historical changes? Consider aging within the Baby Boomers versus aging within Gen X-ers. The Baby Boomers had few of the benefits of improved social attitudes toward healthy eating and fitness that characterize the younger generation as they approach midlife. The Baby Boomers also went through different historical periods that affected their social and political attitudes. Because we can’t pluck people out of their own generation and watch them grow older in a different one, we’ll never know how much any individual, much less an entire age cohort, is showing changes intrinsic to aging separate from those related to these cultural factors.

Average people probably doesn’t fret too much about the limitations of research on aging, but they should. Most of what we read about aging in the popular press ignores the possibility that cultural shifts rather than true age-related changes account for a study’s findings. Do people actually become less well able to remember as they get older? Or is it only that older people now had poorer education when they were young and so never had learning skills as solid as their younger counterparts do now? Even if we follow the same people from youth to old age, we don’t know whether they change as a result of aging or as a result of the historical era in which they lived.

Clearly, then, we need a way to separate age from time. Such a feat would also have tremendous potential benefits for health. What if you didn’t have to lose your physical prowess and health as you got older? If you could slow down the biological time bomb counting down within your body, imagine how much better you would feel.

For decades, scientists who study aging have proposed swappingfunctional age for chronological age as a way out of the age-time quandary. We’ve also thought about asking people to tell us how old they “feel,” or subjective age. This wasn’t a bad idea, but it was not particularly scientific or reliable. Let’s say you’re 28 but you’re coming down with the flu, so you like you’re 48. When you get together you’re your high school pals, though, you feel 18. For a measure of age to perform as an adequate substitute, it has to provide a mood- and illness-resistant estimate.

A biological measure of functional age would seem to have more credibility, but it’s not very practical. Taking all the measurements that you’d need to estimate someone’s functional biological age becomes an expensive and time-consuming operation. In addition to measuring such obvious factors as blood pressure, heart rate, muscle mass, lung expiratory volume, kidney excretion rates, and so on.

To get biological age, you would also need to put people on a treadmill and get their heart and lungs to crank out their maximum capacity- so called “aerobic power.” Even this would not be a complete measure of functional age, but with an average decline of 1% per year after the age of 30 in the ordinary (sedentary) person, you’d have some sort of quantitative index that isn’t completely mixed up with historical era.

Norwegian medical researchers may finally have cracked the code.In a 24-year follow-up study of 37,000 adults, Bjarne M. Nes and his colleagues used a measure of cardiorespiratory fitness based not on actual exercise capacity as measured by aerobic power but instead on the far simpler method of asking people a series of questions, including their age, Body Mass Index (BMI), resting heart rate, and answers to these 3 questions:

  1. How often do you exercise? (5-point scale from never to almost every day)
  2. How hard do you usually push yourself? (3-point scale from not at all to push yourself to exhaustion)
  3. How long do you exercise? (4-point scale from less than 15 to 60 minutes or more)

The cardiorespiratory fitness measure was particularly useful in predicting death from cardiovascular disease among people less than 60 years old. They calculated the odds of dying from cardiovascular disease as well as any cause at all on the basis of 1 standardized unit of fitness defined as a “MET” (metabolic unit) which equals the energy (oxygen) used by the body at rest. The harder your body works during the activity, the more oxygen is consumed. Each MET increase in cardiorespiratory fitness was reduced with as much as a 22% decrease in cardiovascular disease death and 10% less for all causes of death.

In addition to showing that your risk of death is reduced proportionately to the extent that you exercise, the study’s findings allowed the authors to develop a test of fitness age.

The study’s findings show that if we think of age not as years since birth but years prior to death, it’s clear that you can literally become “younger” (have more years left to live) by maintaining this level of fitness. The expression “add more life to your years rather than years to your life” couldn’t be more appropriate.

Although cardiorespiratory fitness was the main focus of this study, physical exercise has other benefits that can keep your brain “younger” as well. Dementia due to Alzheimer’s disease is, at this point in time, not thought to be preventable. In contrast, vascular disease, which is related to cardiorespiratory fitness, can be preventable through exercise. There are also benefits of exercise to your mood, metabolism, and sexual health.

Of course, exercise can’t prevent everything wrong from happening to you, and there in fact can be risks associated with exercise not properly conducted. You can exercise to the point of damaging your joints, you might become obsessed with it, and you might even suffer more pronounced tooth decay than you otherwise would.

By the same token, leading a sedentary existence can make it even more difficult for you to exercise, starting a vicious downward cycle. Once you start to incorporate a reasonable amount of exercise into your lifestyle, though, it can set up a pattern of reinforcement especially if you notice that your mental outlook starts to lift and you start to feel more alert and energetic.

Once you think of your age as a needle you can move down the scale, you can conceive of your own life in a new and more controllable light. Age can truly become, for you, “just a number,” defined by you, and not just the calendar.

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