Older adults may have to work harder than young people to perform the same physical activity, but regular exercise may close that age gap, research findings suggests.

In a study comparing sedentary adults in their 60s and 70s with those in their 20s and 30s, researchers found that older men and women had to use much more oxygen to walk at the same speed as their younger counterparts.

But that was before they went through a six-month exercise program. After taking up walking or jogging, biking and stretching, the senior study participants reversed their loss of exercise "efficiency."

Exercise efficiency refers to how much energy the body expends to perform a given activity. At the start of this study, older men and women used 20 percent more oxygen to walk at the same speed as a younger person, said Dr. Wayne C. Levy of the University of Washington in Seattle, the study’s senior author.

But six months of regular exercise — 90 minutes, three days per week — improved older participants’ exercise efficiency by 30 percent, versus only 2 percent among their younger counterparts.

The findings are published in the current issue of the Journal of the American College of Cardiology.

It’s well known that as people age, there is a decline in exercise capacity — how much work a person can do before becoming exhausted. But the new findings suggest this is not just a product of the aging cardiovascular system being less able to send oxygen to working muscles. The older body also needs more oxygen to perform the same work as a younger one — that is, exercise efficiency declines.

But this decline appears to arise largely from inactivity, and may well be reversible.

The idea that exercise efficiency dips with age is a "relatively new concept," Levy said. And though younger people in his study were still better at pumping blood and oxygen to their muscles after exercise training, it was only the older exercisers who showed significant gains in exercise efficiency.

Their "disproportionately" greater improvement in this area, Levy and his colleagues write, is "new and unexpected."

It’s not clear yet how intensely people need to exercise to hang on to their efficiency as they age, according to Levy. But he said he suspects that any activity done regularly, including walking, would have benefits.