The study, published by online journal Plos One looked at men and women over the age of 65 who either walk or run for exercise.

Researchers from Humboldt State University and the University of Colorado tested two mixed groups of older adults, who were either self-reported walkers or joggers, to see how difficult the participants found it to walk at three different speeds on a treadmill.

They found the adults who ran for exercise had a 7 to 10 per cent better walking economy than the group of walkers - and they had a similar metabolic "cost" to people in their 20s.

They then compared the walking economy between the two groups, and also compared it to  that of young and older adults who had no aerobic training.

"What we found is that older adults who regularly participate in high aerobic activities - running in particular - have what we call a lower metabolic cost of walking than older, sedentary adults. In fact, their metabolic cost of walking is similar to young adults in their 20s," said Justus Ortega, Kinesiology professor at Humboldt State University.

According to Humboldt State, metabolic cost is "the amount of energy needed to move, and naturally increases as we age", and also a "key predictor of morbidity in older adults."

The researchers don't know why the joggers they studied had a better walking economy than the walkers, but the researchers said it seems to keep people younger.

"The bottom line is that running keeps you younger, at least in terms of efficiency," said Rodger Kram, a Professor of Integrative Physiology at the University of Colorado, Boulder, and a co-author of the paper.

In conclusion, the researchers said: "older runners mitigate the age-related deterioration of walking economy."

However, Dr Evangelos Pappas, a senior lecturer of Physiotherapy at the University of Sydney, says while the study is well designed, the authors may have overemphasised their findings.

"The authors may have overstated their conclusion. They say older runners mitigate the age-related deterioration of walking economy, but the study is not  designed to answer that," says Dr Pappas.

Dr Pappas says to be able to say running mitigates the effect of age-related walking economy deterioration, researchers need to take a group of middle-aged people, see who runs and who doesn't, and track them for some time.

He says people should take their findings as conditional evidence that running could improve your ability to get around as you age, but everyone should definitely continue to walk for exercise.

"Walking is great: it's been shown to mitigate many things," says Dr Pappas. "It's been shown to help people with lower back pain and osteoarthritis, so it's good to see a study show walking is a good thing."

Dr Pappas also said this research doesn't mean everyone should take up running either.

"That should be very customised advice, people who have osteoarthritis would be better off with more low-impact activity with walking," says Dr Pappas, adding people with knee or hip problems should also be cautious about taking up running based on this study alone.

He acknowledges it does provide preliminary evidence that you may be conditioning your body for older age, but more research needs to be done.

"It is a preliminary study in sample size and design, it still has be validated," says Dr Pappas.

The researchers say they have future studies planned to look into whether other aerobic activities like swimming and cycling have the same effect on physical decline.