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DALLAS — In the futuristic world of winsome dreams, cheeseburgers have single-digit calories; workouts, single-digit minutes.

Well, hold tight to your jet pack. The magic wand has been waved — not for cheeseburgers, but it seems so for workouts.

Cases in point: Research published in the American College of Sports Medicine’s Health & Fitness Journal touts the effectiveness of a strength-training workout using only body weight and lasting merely 7 — albeit very uncomfortable — minutes.

A Norwegian study found that 4 minutes of high-intensity activity — heart rate at 90 percent of maximum capacity — shares similar benefits to four such efforts separated by 3 minutes of downtime.

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The benefits of high-intensity training have been known for a while, experts tell us. But in our busy lives, new research on shorter and shorter workouts continues to tantalize, especially when compared with the 150 weekly minutes of exercise recommended by the American College of Sports Medicine (ACSM).

“What’s important to remember is that there’s no magic in any of this,” says Allen Jackson, chairman of the department of Kinesiology, Health Promotion and Recreation at the University of North Texas.

The point, he says, “is getting active, the muscle groups you’re working, the specificity of training.”

It’s also the level of intensity, which, in order to make the exercises effective, has to be extreme. Four minutes at 90 percent of maximum heart rate is hardly casual.

“That’s the highest range of intensity that the American College of Sports Medicine recommends,” he says. “The highest! The highest! That’s Michael Phelps!”

The trick of intervals is that they “allow you to do something harder for a short period of time and allow you to build up to that level of intensity,” says Benjamin Levine, medical director of the Institute of Exercise and Environmental Medicine at Texas Health Presbyterian Hospital Dallas. “If it’s just longer periods of lower intensity you do, you’ll never be able to do more.”

“When you do high-intensity aerobic intervals, you have a nice change in the heart,” Levine says. “The heart muscle gets stronger, your muscles get stronger and better able to utilize oxygen.”

If you’re exercising to lose or maintain weight, keep in mind that working out for the 150 recommended minutes spread over a week burns more calories than the shorter bursts.

“More moderate, longer-term exercise will have lower risk for injury. Joggers get injured; walkers don’t very much,” Jackson says. “The drawback? It takes more time, and time is definitely a barrier.”

Also, saying a workout will last 4 minutes, or 7, or even shorter periods of time isn’t entirely accurate, Levine says.

“Of course you have to warm up. There’s recovery between,” he says. “Nobody should think you put on your shoes and in 4 minutes you’ll be finished.”

Additionally, these aren’t workouts just anyone can plunge right into, Jackson says.

“My concerns are about injury and about someone who really isn’t ready to do a high-intensity exercise bout,” he says. “You just can’t start that off. It just isn’t a good idea, especially when you talk about sedentary people going all out.”

He and Levine do agree that shorter stints can have a place in a workout regimen.

“Four minutes,” he says, “would be better than no minutes. But make sure you’re ready to do those 4 minutes.”

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