Less than an extra hour a week of moderate exercise can make a big difference in helping older adults stay mobile and reduce their risk of developing major mobility problems, a U.S. study suggests.

Improvements were seen in all the 70-to-90-year-olds who added some physical activity to their weekly routines over about two years, and those who got more exercise saw greater changes, researchers report in the journal PLoS ONE.

Exercise prevents or improves conditions such as hip fractures, heart disease and diabetes that often underlie mobility disability, said lead author Roger Fielding of Tufts University in Boston. But “it was not known if exercise could prevent the onset of physical disability in older adults who might be at risk for becoming disabled and if the amount of exercise that was performed influenced this response,” he told Reuters Health in an email.

His team found “a graded dose response”, with the greatest benefit “in the group of people who on average increased their exercise approximately 50 minutes per week over two years,” Fielding said.

The researchers studied 1,635 men and women who enrolled in The Lifestyle Interventions and Independence for Elders (LIFE) Study in 2010 and 2011, between ages 70 and 89.

At the start, participants were inactive, with less than 20 minutes of regular physical activity per week.

Half were randomly assigned to a program of walking and walking-based strength, flexibility and balance training. The others were assigned to twice-monthly health education workshops. The study team used movement monitors and self-reporting to measure weekly physical activity in both groups at the start of the study and after 24 months.

After an average of 2.6 years, researchers assessed participants for development of a major mobility disability, which they defined as loss of the ability to walk 400 meters (437 yards) within 15 minutes without sitting, and without a walker or assistance from another person.

In a previous study, the team found that being physically active lowered the risk of any persistent mobility disability by 28 percent and the risk of major mobility disability by 18 percent.

In the current analysis, they found that more activity is better, but even a little helps. Dividing the exercise group into four subgroups based on weekly activity level, researchers found that those with the most activity were 77 percent less likely than those with the least activity to develop major mobility disability.

There was a continuous, graded effect, with the most benefits seen by participants who engaged in at least 48 minutes of physical activity per week.

Moderate intensity exercise is generally safe for most people, Fielding said. “Walking was part of our intervention, and almost all older people, even those with mobility problems, can begin a walking program.”

He recommends starting slowly, with about five minutes per session and building up over time.

“Try to walk most days of the week but at least five,” he said, adding that people should inform their physician that they are starting to exercise but don’t necessarily need to wait for their physician’s okay.

“Older people worried about their mobility should talk to their physician for advice and request an evaluation by a physical therapist, who can help them target areas to strengthen,” said Dorothy Dunlop, a researcher at Northwestern University Feinberg School of Medicine in Chicago, who wasn’t involved in the study.

Enjoyable programs, such as Walk with Ease and Enhanced Fitness, are designed for adults with mobility problems and are widely available through the YMCA and the Arthritis Foundation, she said.

Weight control is also an important key to preventing mobility problems, Dunlop added.