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A mere six minutes of intense, gut-busting exercise a week can do as much to improve a person's fitness as a traditional one-hour-a-day regime, according to startling new findings from Canadian researchers.

If they are right, the approach will strip away the time-honoured excuse of the inactive: "I don't have time to exercise."

The research, which will be published in the June edition of the Journal of Applied Physiology, found that people who undertook "modified interval training" that consisted of cycling at breakneck speed for short bursts boosted their endurance just as much as those who spent hours a week biking at a more moderate pace.

"Short bouts of intense exercise improved muscle and performance to the same extent as traditional endurance training," said Dr. Martin Gibala, an associate professor in the department of kinesiology of McMaster University in Hamilton, Ont.

The study was conducted on 23 subjects, all of whom were recreationally active, but not athletes. They were split into three groups, and made to exercise at varying intensity, based on their maximum aerobic capacity (VO2max).

VO2max is a measure of the amount of oxygen that a person's body can bring into the lungs; that oxygen then moves into the muscles, and creates energy, largely through the conversion of carbohydrates and fat. The higher a person's VO2max, the more fit he or she is considered to be. While genetics play a factor, most people can improve their VO2max substantially with endurance training.

In the study, one group did short interval training on a stationary bike -- 30 seconds of intense bike riding (at 250 per cent of their VO2max), followed by four minutes of rest. They repeated the exercise for a total of two minutes of hard cycling, three times a week.

The second group used modified interval training, where they biked hard (at 100 per of VO2max) for 60 seconds, followed by 75 seconds recovery, for a total of 10 minutes cycling three times a week.

The third group took a more traditional approach, cycling at a moderate level (65 per cent of VO2max) for 90 to 120 minutes, three times a week.

After two weeks of the program, researchers did muscle biopsies and further tests to determine changes in fitness levels. They found that all three groups showed similar improvements in their aerobic capacity.

"We thought the findings were startling because they suggest the overall volume of exercise people need to do is lower than what is currently recommended," Dr. Gibala said.

He said the research could have implications for professional athletes, recreational athletes and even heart patients.

But other fitness experts expressed skepticism that the findings were meaningful to anyone other than a small group of elite athletes.

Dr. Norm Gledhill, a professor in the school of kinesiology and health science at York University, said the research shows only that short interval training can improve one measure of fitness in the short term.

He said it is highly unlikely that most people would be willing to engage in the intense level of activity required, even for brief periods of time, so they should be encouraged to adopt more realistic fitness programs.

"I think most people will walk for 30 minutes a day, and walking 30 minutes a day will provide a lot of benefits for your health," Dr. Gledhill said.

He added that there is also no evidence that intense interval training can lower cholesterol or blood pressure, or help people lose weight and stave off disease, which is far more important to the average person than their VO2max.

Researchers also cautioned that people should not undertake vigorous exercise without first consulting their doctor.

Currently, almost half of Canadians -- 54 per cent of men and 44 per cent of women -- are considered inactive. According to material in the article, physical inactivity costs the Canadian economy approximately $5.3-billion annually.