It may seem obvious, but now there’s proof: Physical activity of moderate intensity can help older people stay mobile and independent, according to the largest clinical trial ever done.

The study, presented Tuesday at the annual meeting of the American College of Sports Medicine in Orlando, Fla., involved researchers at eight field centers.

A physical activity program consisting of aerobic, resistance and flexibility exercises significantly reduced the risk of a major mobility disability, researchers found.

“Until this study, we didn’t have the proof necessary to say that daily exercise, sustained over several years, truly can prevent loss of mobility,” said Anne Newman, chair of the Department of Epidemiology at the University of Pittsburgh’s Graduate School of Public Health, which participated in the study. “Doctors can now feel confident that moderate physical activity improves the independence and mobility of older adults.”

For purposes of the Lifestyle Interventions and Independence for Elders (LIFE) study, a “major mobility disability” was defined as an inability to walk 400 meters, or about a quarter of a mile.

Researchers, led by Marco Pahor of the University of Florida Institute of Aging in Gainesville, randomly assigned 1,635 seniors aged 70 to 89 who were able to walk a quarter of a mile either to the exercise program or to a health education program consisting of workshops and upper extremity stretching exercises.

A geriatrician, Newman supervised nearly two dozen researchers at the Pittsburgh field center and chaired the ancillary studies review committee for the national study.

Moderate physical activity helped aging adults maintain their ability to walk at a rate 18 percent higher than older adults who did not exercise, the study showed. Moreover, there was a 28 percent reduction in people permanently losing the ability to walk easily.

“This large impact on reducing persistent disability is important,” she said. “Beyond simply maintaining mobility, this shows that we can repair a deficit through physical activity.”

When recruited to the study, participants could walk a quarter mile in 15 minutes, but were at risk for losing that ability.

The benefit of physical activity was proportionately greater for the seniors who began the study with the lowest physical function, the researchers found.

Patients with low physical activity are not often recruited for large studies, Pahor said. The LIFE study is important because it provides data on an understudied group.

The exercise program consisted of walking for 150 minutes a week as well as doing strength exercises consisting of leg lifts with ankle weights from a seated position. They did this for two years.

Every six months, research technicians checked the ability of participants to walk, as well as their body weight, pulse rate and other vital statistics.

One participant who saw dramatic results was Josephine Scott, 77, of Pittsburgh.

“I’m so grateful and thankful that I got into this study,” she said. “It got me out of the house and exercising.”