Volunteers who run regularly expend the same amount of energy as a 20-year-old.

Older people who go running several times a week walk with the same vigour as a typical 20-year-old, a study has shown.

But those who only exercise by walking are likely to tire more easily, researchers found.

US scientist Rodger Kram, from the University of Colorado at Boulder, said: “The bottom line is that running keeps you younger, at least in terms of energy efficiency.”

The study involved 30 healthy volunteers with an average age of 69 who either ran or walked regularly for exercise.

In tests, they were asked to walk on a treadmill at three different speeds, 1.6mph, 2.8mph and 3.9mph. During the training sessions, measurements were taken of their oxygen consumption and exhaled carbon dioxide.

Co-author Justus Ortega, from Humboldt State University, California, said: “What we found is that older adults who regularly participate in highly aerobic activities – running in particular – have a lower metabolic cost of walking than older, sedentary adults and also lower than seniors who regularly walk for exercise.

Running keeps you younger, at least in terms of energy efficiency

“It’s been known for a long time that, as people age, their maximum aerobic capacity, or ‘horsepower’, declines, and that is true for runners as well. What’s new here is we found that old runners maintain their fuel economy.”

Volunteers who ran regularly expended the same amount of energy as a normal 20-year-old.

But the amount of energy used by non-runners for walking was typical of older, sedentary adults – about 22 per cent higher than it was for 20-somethings.

Owen Beck, another member of the University of Colorado team, said: “It was surprising to find that older adults who regularly run for exercise are better walkers than older adults who regularly walk for exercise.

“The take-home message of the study is that consistently running for exercise seems to slow down the ageing process and allows older individuals to move more easily, improving their independence and quality of life.”

The research is reported in the online journal Public Library Of Science ONE.