People who complain they have no time to exercise may soon need another excuse. Some experts say intense exercise sessions could help people squeeze an entire week's workout into less than an hour. Those regimens -- also called-- were originally developed for Olympic athletes and thought to be too strenuous for normal people.
But in recent years, studies in older people and those with health problems suggest many more people might be able to handle it. If true, that could revolutionize how officials advise people to exercise -- and save millions of people hours in the gym every week. It is also a smarter way to exercise, experts say.
"High-intensity interval training is twice as effective as normal exercise," said Jan Helgerud, an at the Norwegian University of Science and Technology. "This is like finding a new pill that works twice as well ... we should immediately throw out the old way of exercising."
Studies on intense training have been published in sports medicine journals and have largely been based on young, healthy people. Experts say more studies are needed on how older and less fit populations handle this type of exercise before it can be recommended more widely.
Intense interval training means working very hard for a few minutes, with rest periods between sets. Experts have mostly tested people running or biking, but other sports like rowing or swimming should also work.
Helgerud recommends people try four sessions lasting four minutes each, with three minutes of recovery time in between. Unless you're an elite athlete, it shouldn't be an all-out effort.
"You should be a little out of breath, but you shouldn't have the obvious feeling of exhaustion," Helgerud said.
In Britain and the U.S., officials recommend that people get about 2 1/2 hours each week of moderate exercise. Those guidelines target a mostly sedentary population and are intended to help with weight control and heart health, not boosting fitness levels, increasing strength or endurance.
Some experts have cautioned that ordinary people shouldn't substitute their regularfor intense training.
"There isn't enough evidence to say people should do one or the other," said Gary O'Donovan, a sports and exercise expert at the University of Exeter. "Any bout of exercise has the potential to improve your blood pressure or lower your cholesterol, and it doesn't necessarily have to be intense."
Still, O'Donovan said more intense exercise would probably produce better benefits.
Helgerud says the time people spend in the gym could be slashed dramatically if they did interval training instead. He said officials have been too afraid of recommending intense training for fear it would be too much for some people.
"I'm much more afraid of people not exercising at all," he said. "Inactivity is what's killing us."