London ? 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 interval training — 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 exercise expert 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.