Seventy and Going Strong

Muscle wasting poses serious problems for many seniors. But until scientists studying the biological roots of muscle loss find a cure, exercise remains the best way to beat the blight

Young athletes bulk up to crush the competition, but iron-pumping old timers tend to relish humbler victories. According to Lee Marken, a 76-year-old retired psychologist who teaches muscle toning for seniors at the YMCA in San Rafael California, a student once interrupted the class to share her excitement over her recent improvement in strength. "I opened a jar," the woman proclaimed.

For many seniors, wrestling the lid off the jelly jar is no small triumph. Skeletal muscles--such as those in the arms, hands, and legs--shrink and weaken with age, sapping many elders of the strength needed to perform basic tasks such as getting out of a chair or pushing a lawnmower. Scientists are laboring to unravel the mechanisms that underlie age-related muscle atrophy, but thus far they've failed to come up with any pharmaceutical fixes. Until they do, some researchers say that sticking to the familiar maxim "use it or lose it" could be our best bet for keeping muscles strong.

Muscles don't fade overnight. In most cases, they start going kaput well before retirement. After peaking in young adulthood, muscle mass begins to sag in our 40s and drops by about 50% over the next 4 decades. A late-1970s study of more than 2500 seniors showed that about half of women over 65 could not lift 10 pounds--the weight of a typical grocery bag. Men also lose brawn, but the change poses more trouble for women, who start with less muscle mass than do their male counterparts.

Loss of muscle mass--or sarcopenia--catches many off-guard, particularly those in sedentary careers, says Alfred Fisher, a geriatrics physician at the University of California San Francisco. Those who do notice their muscles languishing "often ascribe it to being busy or not having time to work out." As a result, they don't take initiative to curb the decline.

But research shows that exercise can slow sarcopenia, even when started in later life. In a 1994 study of 100 nursing home residents aged 72 to 98 years, researchers found that participants who lifted weights saw their muscle strength double after just 10 weeks of training. Nonexercisers who gulped protein-rich drinks to build muscle tissue saw no strength gains.

The age-related atrophy of muscle tissue originates within muscle cells themselves. The bundles of contractile fibers that give muscles their stretch begin to vanish. And the fibers that remain start to shrivel and don't produce the power they did in their youth.

But what drives this decline remains a matter of some debate. Biochemist Ewa Prochniewicz of the University of Minnesota, Minneapolis, pins part of the blame on accumulated damage to actin and myosin, the proteins that drive muscle contraction. Examining leg muscles of young and old rats, Prochniewicz and colleagues discovered that myosin from aged muscles sustained more wreckage than did the same protein in young muscles. The type of injury points to the work of oxygen radicals, byproducts of metabolism that are believed to be involved in aging of many tissues (see "Villain or Victim?"). The results suggest that antioxidants can reverse these sorts of myosin impairments and keep muscles healthy--studies that Prochniewicz plans to conduct in the future.

Another theory for why muscles fizzle with age builds on the "use it or lose it" hypothesis. Muscles contract only after they've received the go-ahead from embedded nerves--nerves that don't fire as vigorously in older adults. Thus, aging muscles receive fewer nerve signals and eventually die from disuse. The idea that regular activity sustains a muscle's health gained support from recent work by John Faulkner of the University of Michigan, Ann Arbor, and colleagues. The researchers surgically disabled the nerves within the leg muscles of rats so the muscles could contract only when stimulated artificially. Rats whose muscles received 2 months of electrical stimulations showed much less decline in muscle mass and force compared to rats whose muscles were left untouched. Although the zapping did not prevent loss of individual muscle fibers, it preserved muscle mass by bolstering the size of the fibers that remained. If the findings hold true for people, they suggest that lethargic middle-agers who take up weight training later in life won't regain the muscles they've lost, but should be able to make the most of the muscle that remains, says Faulkner.

But injured muscles can repair themselves by building new fibers, at least in younger people, and some scientists are testing whether aging muscles weaken because they lose this regenerative capacity. Neurogerontologists Jan-Erik Edström and Brun Ulfhake of the Karolinska Institute in Stockholm, Sweden, categorized a group of aging rats as either "well-preserved" or "severely affected" based on their performance on standard tests of strength and balance. Surprisingly, they found that the leg muscles from the gimpier rats appeared to have tried harder to mend themselves: They contained larger quantities of proteins that jump-start muscle development than did the better preserved muscles. Why muscles poop out in spite of their apparent potential for restoration remains unclear, Edström says.

Part of the problem could lie in chemical messengers whose quantities shift with age. For example, concentrations of testosterone, a hormone that boosts muscle mass and strength, decline with age--in both women and men. At least one company, GTx Inc. in Memphis Tennessee, is trying to combat sarcopenia by developing drugs that mimic testosterone's muscle-building effects. Phase I clinical trials of one such compound began in February.

Whether such treatments will work in seniors, however, is unclear. Previous research has shown that testosterone supplements don't boost muscle strength in seniors nearly as much as they do in younger adults. "You get less bang for your buck in the older person," says Fisher.

Even if a drug that slows sarcopenia does come to market, experts still recommend building muscles the old-fashioned way. Seniors seem to be getting the message about the importance of exercise in retaining muscle, but "what we haven't done a great job of yet is figure out strategies to make them participate in exercise and get involved in exercise programs on a regular basis," says physiologist Roger Fielding of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston. "There's no one drug that could purport to have all the behavioral, psychosocial, and physiological effects of exercise and physical activity." Without a little sweat, the joys of jar-opening just wouldn't be as sweet.

San Francisco Area writer Esther Landhuis expects to begin compulsory weight training in several months with the arrival of her first child.