These athletes are effectively interval training. Every time they leap out of the starting block their bodies are experiencing an explosion of intense activity for a short time.

For one hundred metres they're pushing themselves to the limit, then they stop for a few seconds and start again. It's this repetition, combined with extreme exertion, that increases their heart rate to the point where their bodies begin to adapt, so the next time they exercise they can do even more.

It's called interval training because you can't go flat out like these cyclists for long periods. After a few seconds to catch their breath, they're at it again, pushing themselves to the limit. This is what most people do in the gym.

But even an hour's stint on these cross trainers doesn't count as intense exercise. It's easy to see why interval training was originally developed for Olympic athletes. At the time it was thought to be too strenuous for non-athletes. But now there's an increasing amount of evidence from physiologists that all of us can do interval training.

Dr Richard Godfrey, who teaches sports science here at Brunel University in London, says it can benefit all of us immensely. Studies at universities like this one show people doing interval training can double their endurance, improve their oxygen use and strength by more than 10 percent, and their speed by at least 5 percent. That's compared to normal exercise like jogging.

But Godfrey argues that it isn't easy to achieve this level of activity. Many people might think they're doing an intense workout, but they're not. Just because you break out in a sweat doesn't necessarily mean your getting your heart rate high enough.

In health terms interval training could backfire, because if you're not doing it properly you get less exercise and you don't get the specific benefits that come from the intensity of the activity.

Dr. Godfrey says "we're talking about exercise up to 90% of maximum heart rate. These are really high intensity efforts, this is where you really can't talk, you are unable to maintain a conversation, it's hard effort and psychologically it's very tough."

Dr. Godfrey argues that while we can all gain from interval training, it shouldn't be undertaken carelessly. He advises that anyone, who has been ill, overweight, or who simply hasn't exercised much in the past should get a full health screen before they start pushing the boundaries of what their bodies are capable of.

Godfrey advises that people should first "begin low level exercise building up over a period of three to six months to improve their fitness, to improve the muscles, the bone, all of those sorts of things."

It's been suggested by the Norwegian University of Science and Technology that thirty minutes of this sort of intensive exercise is all we need. It claims long gruelling workouts in the gym aren't necessary and should be obsolete. Such an exercise revolution would mean that even the busiest people in our society can get in their quota of exercise. It very different to official guidelines in many countries.

The British and American governments, for example, recommend that people get at least two hours of moderately strenuous exercise each week.

What's more, the Norwegian study argues that even studies in the elderly and in heart patients found they had better oxygen use and fitness after doing interval training. Experts say intense bursts of activity are precisely what the body needs to build stronger muscles. Traditional workouts lasting an hour or more simply don't push the body enough.

These students say they've seen vast improvements using interval training. Edward West is a second year sports science student and he's used the regime to improve his rugby. West, who plays full back for Brunel's first team, says he needs to be able to catch the ball from a kick and then do a short, but fast, thirty to forty metre sprint, so interval training matches what he has to do on the rugby pitch.

He says he knows when his heart has reached 95% of its capacity and says "it's not so much pain, but I get this feeling in my stomach, like you feel it and you think oh, do I feel a bit sick".

According to Norwegian scientists people who aren't athletes should do four sessions lasting four minutes each, with three minutes of recovery time in between, and this, they claim, should leave you a little out of breath, but not exhausted.

That's not how West feels during the second half of a match. He says "you're sort of a bit out of breath and then you're body, you feel the lactic acid build up and your body feels a bit light, you go and do that forty metre burst and you can really feel it like in here, almost like a little bit sick."

Godfrey is concerned by claims that the short burst of intensive activity can replace two hours of regular exercise. He says we need to move our bodies more not less and interval training should be seen as an addition to other activities.

Most sports scientists want more research to come up with definitive regimes for people generally. They agree intense bursts of exercise help the body to convert one type of muscle fibre into another type that uses oxygen more efficiently and is capable of exercising a lot longer.

It's believed the higher metabolism experienced after interval training lasts for several hours, slowing as the body burns fat and carbohydrates.

So next time you're pushed for time at the gym, just go faster. But according to scientists here it might not be wise to give up the cross trainer yet.

AP