Dolores "Lolly" Selenkow is no ordinary octogenarian. The 86-year-old Newton grandmother hits the gym five days a week, plays tennis one or two days, and still works part time managing her family's real estate business.
Longevity tends to run in Selenkow's family — her father died at age 99 and she has an aunt who is 101 — but Selenkow says "being active and having a good attitude" helps.
A December US Census Bureau report suggests Selenkow is in the minority of older Americans. The report found that 39 percent of people over age 65 battle at least one disability, and the most common hurdle they face is serious difficulty walking or climbing stairs.
The ranks of older, disabled adults could swell rapidly, the report cautioned, as the number of aging baby boomers increases. Such disabilities mean more Americans losing independence and relying on costly, long-term health services.
Which is why researchers in Boston and across the country are redoubling efforts to pinpoint the elders most likely to become disabled, and craft simple exercise programs to stem the downward slide.
Dr. Jonathan Bean, an associate professor at Harvard Medical School and a researcher at Spaulding Rehabilitation Network, is tracking about 350 older adults, including Selenkow, and has found that building core — also known as abdomen — strength, and leg speed are vital to keeping elders active and independent.
Most programs, he said, tend to focus on leg strength and flexibility in knees and ankles. But a strong core and the ability to walk quickly can mean the difference between an elder being able to walk across the street before a traffic light changes, and being homebound, relying on someone else to run errands, he said.
Now, Bean is working with researchers at Boston University to measure the effectiveness of a program that teaches elders exercises via an iPad. It is designed to improve their mobility and assess their performance through videos and live online chats with therapists. The theory is that it will help seniors who have trouble getting to a physician's office stick with rehab longer while saving money — for the patient and the health care system.
"Medicine needs to look through a different lens in order to help people in the best way possible," Bean said.
Another study, the largest and longest-running trial of its kind, found that regular physical activity in older adults measurably reduced mobility problems compared with a program that offered health education and stretching exercises.
The study included roughly 1,600 sedentary volunteers, age 70 to 89, who already had mobility problems. It was conducted in eight health centers across the country, including Tufts University, and followed the participants for nearly three years.
Elders in the activity group worked toward a goal of walking 2½ hours weekly, in addition to 20 minutes daily improving balance, leg strength, and flexibility through exercises they were taught to do at home.
"Many of these people could not walk two, or three, or four minutes without stopping, but by the end, many could walk 20 to 30 minutes," said Roger Fielding, senior scientist and director of Tufts's Nutrition, Exercise Physiology, and Sarcopenia Laboratory, and lead researcher of the Boston section of the study.
"The thing older people fear the most is losing their independence," Fielding said. "This showed that a regular, structured program of physical activity could preserve independence, even in at-risk older adults."
Postponing nursing home admissions by six months, for instance, could have a tremendous impact on health care costs, said Dr. Jack Guralnik, who spent 25 years studying disabilities at the National Institute on Aging.
Roughly $134 billion was spent in 2011 for nursing home care in the United States, according to a report by the Congressional Budget Office.
"Many older people will have an event, a catastrophic hip fracture, or a stroke, and it's obvious how they became disabled," said Guralnik, now a professor at the University of Maryland School of Medicine.
"But many older people kind of drift downhill, and we don't really understand how they got there," Guralnik said. "We can't really intervene, until we understand it better."
Kay Lazar can be reached at Kay.Lazar@globe.com.