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NYT

Very intense exercise, as little as 12 minutes total over a two-week period, can double endurance capacity, according to a study published in the June issue of the Journal of Applied Physiology.

Sixteen physically active college students ages 21 to 27 took part in the study. Eight were tested two weeks apart with no training in between. The other eight performed “sprint interval training” – they did four to seven 30-second sprints on a stationary bicycle, resting four minutes between each sprint. A researcher encouraged them verbally to pedal as hard as possible. They performed six of these sessions over two weeks.

The results were surprising. The average improvement in cycle endurance, measured by time to fatigue, was about 100 percent (from 26 minutes at the beginning of training to 51 minutes at the end). The group that did not train showed no improvement.

This kind of training, at least in its most demanding form, may not be for everyone. “We’re not suggesting that totally sedentary people jump on a bicycle and start pedaling their hearts out,” said Martin J. Gibala, the senior author of the paper, “and we’re not suggesting that people do only six minutes of exercise per week. But interval training is not just for elite athletes. Studies have shown that the elderly, and even people with coronary artery disease, can benefit from a properly supervised interval training program.”

Dr. Gibala, who is a professor in the kinesiology department at McMaster University in Hamilton, Ontario, suggested that even people whose only exercise is walking might improve their endurance by simply walking a bit faster for alternating intervals of time. “The main message,” he said, “is that people can get away with less exercise time if they are willing to trade duration for intensity.”

Researchers are uncertain why the training has such a big effect, but it probably stimulates changes in muscle function and blood circulation that increase endurance by metabolizing oxygen more efficiently.