Athletes have been utilizing interval training—alternating periods of high- and low-intensity exercise—for years. (When I wrote last summer about the favorite workouts of 11 Olympians, a number of them cited intervals.) But it has taken a little longer for the concept to trickle down to the average exerciser. Studies have shown that this kind of workout, which has the appeal of taking far less time than the usual steady slog, can improve cardiovascular capacity and other markers of health. Today, researchers are reporting that a workout centered around just two to three minutes of all-out sprinting helped sedentary young men improve their body's capability to process sugar, key to preventing diabetes.
To be sure, the study was small—just 16 men in the active arm—and it is too early for public-health authorities to turn on a dime and start endorsing shorter, more intense bursts of exercise in lieu of the 150 minutes a week of moderate-intensity activity they now recommend. But the potential health benefits of interval training are intriguing.
In this study, subjects used exercise bikes to perform six sessions of intervals over two weeks. Each session consisted of between four and six 30-second sprints, plus a few minutes of rest in between. After two weeks of training, their body's ability to control blood sugar levels improved by 23 percent, says James Timmons, the study's coauthor and an exercise biologist at Heriot-Watt University in Edinburgh, Scotland. The study appears in BioMed Central's BMC Endocrine Disorders.
The amount of exercise burned up only about 250 calories a week. So while there is some early evidence that interval training triggers a mechanism that helps the body burn more fat than steady aerobics, Timmons says that it is "absolutely not" a path to painless weight loss. However, many folks are not losing weight even when they work out 30 minutes or more a day. We may overcompensate by eating more food when we exercise steadily, says Conrad Earnest, director of exercise biology at the Pennington Biomedical Research Center in Baton Rouge, La., who has written about interval training and blood sugar. It would be interesting, he says, to see if interval training had a different effect on weight control over the longer term.
And, says Timmons, two of the major reasons we try to combat obesity are to prevent cardiovascular disease and diabetes; so while interval training may not produce dramatic weight loss unless combined with dietary changes, it may produce those other physiological benefits. Moreover, you can't lose weight on an exercise plan if you don't follow it; it might be much easier for people to do a few sessions of sprints every week than for them to stick to 150 minutes-plus of walking.
The volunteers in this study were young men, and it's folks in their 20s, 30s, and 40s for whom Timmons thinks this kind of workout will be most helpful, in terms of preventing chronic disease. If you know you don't have any health problems and are in your early 50s and younger, he says, you can probably take up interval training with little concern. (If you're in any doubt, check with your doctor about whether you're cleared for such intense exercise.) Just be careful of injuries; adding speed work to running can cause tendonitis or other overuse injuries. To mimic the circumstances of this study, Timmons recommends you use a bicycle, stationary bicycle, or stair-stepping machine, or that you run up stairs. (Downhill running may cause muscle damage that blunts some of the effects, he says.)
It's probably best to build up at least some kind of regular fitness routine before you start, says Earnest, and then add intervals slowly until your sprinting sessions are as long as the rest period. Depending on how hard you're working, intervals can range from 30 seconds to 5 minutes. Or you can just add periods of harder intensity into your existing aerobic workout.
While science is only beginning to investigate the health effects of interval training, its utility now is clear as a time-saving trick to get more from your workout. "People might think, 'If I like to run or bike or walk for an hour and I'm on the road for work, can I do a half-hour at the gym and get the same benefits?' " says Earnest. With intervals, "you can, and you might actually get a little better."