McGuff and Westcott both say it's OK to do other forms of exercise during the week. "I make a distinction between exercise and recreation," McGuff says. "Distilled, pure exercise like SuperSlow does not provide much stress relief and socialization."

Hutchins, however, is pretty down on so-called "aerobics" and has written several books on the subject, including Aerobics Is Dead. (He also disdains the term "cardio.") He relies on biochemistry to explain the cardiovascular benefits of SuperSlow. "People who push so-called aerobics," he scoffs, "think you can cut the heart out and put it on a treadmill. The heart is an involuntary muscle: It will pump harder when there is more blood to pump, and some informal studies have shown that SuperSlow returns more blood to the heart."

Another benefit, according to Hutchins, involves cholesterol. "When you stop to think about it -- what tissue has the most cells, blood, nerves, and chemistry? Skeletal muscles." When you stress the muscle to the point of failure, it brings on a growth mechanism to build more muscle, he says. But that isn't all. He claims that a doctor in Texas is finding that the metabolics of muscle failure are raising HDL, the "good" cholesterol, and may lower the bad stuff, LDL, somewhat. Another researcher, Hutchins says, finds that SuperSlow increases bone density 1% a month: No other exercise is known to come close to this result.

"None of this is really tested," concedes Hutchins. Many people find SuperSlow too challenging. Others say it's not only difficult, but boring. "It's boring? It's boring?" exclaims Hutchins. "That's like saying you don't want to brush and floss because it's not fun."

"It's intense, but not horrible," McGuff says. "Some eat it up. Others I think could go further, but they shut down." In Westcott's trials, only one of his 150 participants stuck with it. He himself quit, saying he was not motivated. "I talked to some Army drill sergeants about it last week," Westcott says. "Maybe they would be able to take it. You need to be pretty tough."