Just six minutes of intense exercise a week does as much to improve a person's fitness as a regime of six hours, according to a study.

Moderately healthy men and women could cut their workouts from two hours a day, three times a week, to just two minutes a day and still achieve the same results, claim medical researchers.

The two-minute workout requires cycling furiously on a stationary bike in four 30-second bursts. Professor Martin Gibala, the author of the study, said:

"The whole excuse `I don't have enough time to exercise' is directly challenged by these findings. This has the potential to change the way we think about keeping fit.

"We have shown that a person can get the same benefits in fitness and health in a much shorter period if they are willing to endure the discomfort of high-intensity activity.''

The study, published in this month's Journal of Applied Physiology, in-volved 23 men and women aged between 25 and 35 who were tested to see how long it took them to cycle 30 kilometers. The subjects, who all did some form of regular moderate exercise, were then given varying exercise programmes three times a week.

The first group cycled for two hours a day at a moderate pace. The second group biked harder for 10 minutes a day in 60-second bursts. The last group cycled at an intense sprint for two minutes in 30-second bursts, with four minutes of rest between each sprint.

At the end of the two weeks each of the three groups was asked to repeat the 30km cycling test. Every subject was found to have improved to the same degree. Further tests showed that the rate at which the subjects' muscles were able to absorb oxygen also improved to the same level.

The key findings in terms of overall health showed that the two-minute workout produced the same muscle enzymes - essential for the prevention of type 2 diabetes - as riding 10 times as long. That is significant in the light of growing levels of unfitness.

Obesity has trebled in Britain since 1982, leading to a rise in type 2 diabetes. The Department of Health estimates that unfit Britons cost the country 2 billion (HK$28.23 billion) a year in the treatment of heart disease and other related illnesses.

Gibala, of the health department of McMaster University in Ontario, Canada, said: "We thought there would be benefits but we did not expect them to be this obvious. It shows how effective short intense exercise can be.''

Three employees of the Reebok Sports Club in Canary Wharf, London, were asked to compare the workouts.

Angie Du Plessis, 35, who rode for 10 minutes in 60-second sprints, said: "It felt like I had just done an hour's run. It was more than I was used to but I feel more exhilarated because it was so intense. It was not much fun and unless I was really pressed for time I would not change my exercise regime.''

Chris Mackie, 23, tried the two minutes of cycling in 30-second super-bursts and found he was exhausted very quickly. "I overworked myself well beyond what I would normally do,'' he said. "I can't believe it. All my energy drained so quickly.

"It was torture but I was amazed at how short a time it took me to tire myself out completely. I didn't enjoy it but it felt like it worked.''

Jules Wall, 27, who rode for 45 minutes at a moderate pace, insisted she had also received a good workout.

"I am not sure I would want to go through the pain of 30-second sprints,'' she said.

The guinea pigs were all quite fit. The authors of the study caution that anyone considering taking up cycling or running at breakneck speeds should first consult their doctor or a fitness instructor.

David Crottie, a fitness expert for Reebok, was confident the program would be effective for anyone with the correct preparation.

"We have never tried it to this intensity before but I agree with the findings,'' he said. "Most people do not want to do it because it is so uncomfortable, but for those willing to endure the intensity it would work.''

Jonathan Edwards, the Olympic triple-jump gold medalist, said: "Everyone seems to be short of time. If people could get fit in a much quicker period I am sure that would encourage more people to do it.

"Going for a 40-minute run is not for everybody. The idea of doing a short intense workout would appeal to people and help them to embrace a healthier lifestyle.''