13-1 What physical changes occur during middle and late adulthood?

Like the declining daylight after the summer solstice, our physical abilities—muscular strength, reaction time, sensory keenness, and cardiac output—all begin an almost imperceptible decline in our mid-twenties. Athletes are often the first to notice. World-class sprinters and swimmers peak by their early twenties. Baseball players peak at about age 27—with 60 percent of Most Valuable Player awardees since 1985 coming ±2 years of that (Silver, 2012). Women—who mature earlier than men—peak earlier. But most of us—especially those of us whose daily lives do not require top physical performance—hardly perceive the early signs of decline.

Athletes over age 40 know all too well that physical decline gradually accelerates. During early and middle adulthood, physical vigor has less to do with age than with a person’s health and exercise habits. Many of today’s physically fit 50-year-olds run 4 miles with ease, while sedentary 25-year-olds find themselves huffing and puffing up two flights of stairs.

Aging also brings a gradual decline in fertility, especially for women. For a 35- to 39-year-old woman, the chances of getting pregnant after a single act of intercourse are only half those of a woman 19 to 26 (Dunson et al., 2002). Men experience a gradual decline in sperm count, testosterone level, and speed of erection and ejaculation. Women experience menopause, as menstrual cycles end, usually within a few years of age 50. Expectations and attitudes influence the emotional impact of this event. Is it a sign of lost femininity and growing old, or liberation from menstrual periods and fears of pregnancy? For men, too, expectations can influence perceptions. Some experience distress related to a perception of declining virility and physical capacities, but most age without such problems.

With age, sexual activity lessens. Nevertheless, most men and women remain capable of satisfying sexual activity, and most express satisfaction with their sex life. This was true of 70 percent of Canadians surveyed (ages 40 to 64) and 75 percent of Finns (ages 65 to 74) (Kontula & Haavio-Mannila, 2009; Wright, 2006). In another survey, 75 percent of respondents reported being sexually active into their eighties (Schick et al., 2010). And in an American Association of Retired Persons sexuality survey, it was not until age 75 or older that most women and nearly half of men reported little sexual desire (DeLamater, 2012; DeLamater & Sill, 2005). As Alex Comfort (1992, p. 240) jested, “The things that stop you having sex with age are exactly the same as those that stop you riding a bicycle (bad health, thinking it looks silly, no bicycle).”

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Is old age “more to be feared than death” (Juvenal, The Satires)? Or is life “most delightful when it is on the downward slope” (Seneca, Epistulae ad Lucilium)? What is it like to grow old?

SENSORY ABILITIES, STRENGTH, AND STAMINA Although physical decline begins in early adulthood, we are not usually acutely aware of it until later in life, when the stairs get steeper, the print gets smaller, and other people seem to mumble more. Muscle strength, reaction time, and stamina diminish in late adulthood. As a lifelong basketball player, I [DM] find myself increasingly not racing for that loose ball. But even diminished vigor is sufficient for normal activities.

With age, visual sharpness diminishes, as does distance perception and adaptation to light-level changes. The eye’s pupil shrinks and its lens becomes less transparent, reducing the amount of light reaching the retina: A 65-year-old retina receives only about one-third as much light as its 20-year-old counterpart (Kline & Schieber, 1985). Thus, to see as well as a 20-year-old when reading or driving, a 65-year-old needs three times as much light—a reason for buying cars with untinted windshields. This also explains why older people sometimes ask younger people, “Don’t you need better light for reading?”

The senses of smell and hearing also diminish. In Wales, teens’ loitering around a convenience store has been discouraged by a device that emits an aversive high-pitched sound almost no one over 30 can hear (Lyall, 2005).

HEALTH As people age, they care less about what their bodies look like and more about how their bodies function. For those growing older, there is both bad and good news about health. The bad news: The body’s disease-fighting immune system weakens, making older adults more susceptible to life-threatening ailments such as cancer and pneumonia. The good news: Thanks partly to a lifetime’s accumulation of antibodies, people over 65 suffer fewer short-term ailments, such as common flu and cold viruses. One study found they were half as likely as 20-year-olds and one-fifth as likely as preschoolers to suffer upper respiratory flu each year (National Center for Health Statistics, 1990).

THE AGING BRAIN Up to the teen years, we process information with greater and greater speed (Fry & Hale, 1996; Kail, 1991). But compared with teens and young adults, older people take a bit more time to react, to solve perceptual puzzles, even to remember names (Bashore et al., 1997; Verhaeghen & Salthouse, 1997). The neural processing lag is greatest on complex tasks (Cerella, 1985; Poon, 1987). At video games, most 70-year-olds are no match for a 20-year-old.

Slower neural processing combined with diminished sensory abilities can increase accident risks. As FIGURE 13.1 indicates, fatal accident rates per mile driven increase sharply after age 75. By age 85, they exceed the 16-year-old level. Older drivers appear to focus well on the road ahead, but attend less to vehicles approaching from the side (Pollatsek et al., 2012). Nevertheless, because older people drive less, they account for fewer than 10 percent of crashes (Coughlin et al., 2004).

Brain regions important to memory begin to atrophy during aging (Fraser et al., 2015; Schacter, 1996). The blood-brain barrier also breaks down beginning in the hippocampus, which furthers cognitive decline (Montagne et al., 2015). No wonder adults, after taking a memory test, feel older. “[It’s like] aging 5 years in 5 minutes,” jested one research report (Hughes et al., 2013). In early adulthood, a small, gradual net loss of brain cells begins, contributing by age 80 to a brain-weight reduction of 5 percent or so. Earlier, we noted that late-maturing frontal lobes help account for teen impulsivity. Late in life, some of that impulsiveness seems to return as inhibition-controlling frontal lobes begin to atrophy (von Hippel, 2007). This helps explain older people’s occasional blunt questions and comments (“Have you put on weight?”). But good news: The aging brain is plastic, and partly compensates for what it loses by recruiting and reorganizing neural networks (Park & McDonough, 2013). During memory tasks, for example, the left frontal lobes are especially active in young adult brains, while older adult brains use both left and right frontal lobes.

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EXERCISE AND AGING Exercise helps counteract some effects of aging. Physical exercise not only enhances muscles, bones, and energy and helps to prevent obesity and heart disease, it also stimulates brain cell development and neural connections, thanks perhaps to increased oxygen and nutrient flow (Erickson et al., 2013; Fleischman et al., 2015; Pereira et al., 2007). Exercise aids memory by stimulating the development of neural connections and by promoting neurogenesis, the birth of new hippocampus nerve cells. And it increases the cellular mitochondria that help power both muscles and brain cells (Steiner et al., 2011).

Sedentary older adults randomly assigned to aerobic exercise programs exhibit enhanced memory, sharpened judgment, and reduced risk of significant cognitive decline (DeFina et al., 2013; Liang et al., 2010; Nagamatsu et al., 2013). Exercise also helps maintain the telomeres (Leslie, 2011). These tips of chromosomes wear down with age, much as the end of a shoelace frays. Telomere wear and tear is accelerated by smoking, obesity, and stress. Children who suffer frequent abuse or bullying exhibit shortened telomeres as biological scars (Shalev et al., 2013). As telomeres shorten, aging cells may die without being replaced by perfect genetic replicas (Epel, 2009).

The message is clear: We are more likely to rust from disuse than to wear out from overuse. Fit bodies support fit minds.