They were hoping to discover whether specific physiological markers could be used to determine age. But they found that it was difficult to tell who was older.

“If you couldn’t see these people many of these functions would point them to a much younger age,” said Professor Stephen Harridge, Director of the Centre of Human & Aerospace Physiological Sciences at Kings College.

“By exercising you do what your body wants it to do and are allowing to age optimally.

“So it is not ageing itself which brings about poor function and frailty, but the fact that people have stopped exercising and are no longer active.”

The 84 male and 41 female cyclists picked for the study had to be able to cycle 100km in under 6.5 hours and 60km in 5.5 hours, respectively, to be included in the study.

Smokers, heavy drinkers and those with high blood pressure or other health conditions were excluded.

The cyclists underwent two days of laboratory testing at King’s which measured cardiovascular, respiratory, neuromuscular, metabolic, endocrine and cognitive functions, bone strength, and health and well-being.

Volunteers’ reflexes, muscle strength, oxygen uptake during exercise and peak explosive cycling power were also measured.

The results of the study showed that in these individuals, the effects of ageing were far from obvious, with people of different ages having similar levels of function such as muscle strength, lung power and exercise capacity.

The maximum rate of oxygen consumption showed the closest association with age, but even this marker could not identify with any degree of accuracy the age of any given individual.

In a basic test which measured the time taken to stand from a chair, walk three metres, turn, and sit back down, even the oldest cyclists were well within the range of healthy young adults.

Although the researchers chose cyclists most other forms of aerobic activity would produce similar results.

Emeritus Professor Norman Lazarus, a member of the King’s team and also a cyclist, said: “Inevitably, our bodies will experience some decline with age, but staying physically active can buy you extra years of function compared to sedentary people.

“Cycling not only keeps you mentally alert, but requires the vigorous use of many of the body’s key systems, such as your muscles, heart and lungs which you need for maintaining health and for reducing the risks associated with numerous diseases.”

The new research was welcomed by charities who urged people to stay active.

Jane Tadman at medical research charity Arthritis Research UK said “The findings of this study back up our own research in the fact that many symptoms associated with ageing such as frailty are caused by being physical inactive. So many of our population are now living well into their 70s and 80s, and that should be a cause for celebration.

“But unless we can ensure that old age is spent in good health through remaining active, and this doesn’t necessarily meaning visiting the gym, it could be climbing the stairs on a regular basis, it will be a stage in life that is endured rather than enjoyed”.