A few years ago, researchers at the National Institute of Health and Nutrition in Japan put rats through a series of swim tests with surprising results. They had one group of rodents paddle in a small pool for six hours, this long workout broken into two sessions of three hours each. A second group of rats were made to stroke furiously through short, intense bouts of swimming, while carrying ballast to increase their workload. After 20 seconds, the weighted rats were scooped out of the water and allowed to rest for 10 seconds, before being placed back in the pool for another 20 seconds of exertion. The scientists had the rats repeat these brief, strenuous swims 14 times, for a total of about four-and-a-half minutes of swimming. Afterward, the researchers tested each rat's muscle fibers and found that, as expected, the rats that had gone for the six-hour swim showed preliminary molecular changes that would increase endurance. But the second rodent group, which exercised for less than five minutes also showed the same molecular changes.
The potency of interval training is nothing new. Many athletes have been straining through interval sessions once or twice a week along with their regular workout for years. But what researchers have been looking at recently is whether humans, like that second group of rats, can increase endurance with only a few minutes of strenuous exercise, instead of hours? Could it be that most of us are spending more time than we need to trying to get fit?
The answer, a growing number of these sports scientists believe, may be yes.
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