Thursday, September 3, 1998 Published at 23:57 GMT 00:57 UK
Exercise helps you live longer - official
Jogging is an aerobic exercise which can improve health
Keeping fit ensures continuing good health and cuts the risk of death from conditions such as heart disease.
It may sound obvious, but research published in a medical journal makes it official.
Until now there has been no hard evidence to prove that fitness benefits long-term health.
However, The Lancet this week publishes the results of a 22-year study of physical activity in middle-aged men.
The research, carried out by a Norwegian team of doctors, concluded that there was a firm link between physical fitness and a reduced risk of death.
The study says people do not have to spend all day in the gym to gain significant benefits, and that those who have let their fitness slip have the most to gain.
The benefits include a reduced likelihood of heart disease and improved breathing ability.
Meanwhile, those men whose fitness continued to decline were more likely to die.
The study's authors called for their findings to influence public health policy.
They also pointed out that while many people rely on drugs and medical treatments to maintain their health, this study established that exercise could be equally beneficial.
Dr Keith Hopcroft, a GP in Essex with an interest in exercise medicine, welcomed the findings. He said: "This is something GPs have been telling patients for a long time.
"In a climate of evidence-based medicine it will help to have something like this."
The team started their work in 1972. Over a three-year period they examined more than 2,014 men aged between 40 and 60 years old, and established how fit they were.
They repeated the process from 1980 to 1982, and monitored the remaining participants until the end of 1994.
Those whose fitness improved over the time of the study were less likely to die. They showed a corresponding improvement in risk factors such as blood pressure, breathing capacity and heart rate.