A study of the potency of super-quick workouts has revealed that a mere four seconds of all-out exercise, repeated two or three dozen times, could be all for many to build and maintain fitness, strength, and physical power. Recent studies show that four-second interval workouts beneficially affect metabolism and muscles in adults of various ages.

People, who are into fitness, usually engage in high-intensity interval training (HIIT). A typical HIIT workout involves repeated, short bursts of arduous effort, known as intervals, interspersed with rest periods.

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According to the study, athletes interval trained to amp their speed and performance. But for most of us, HIIT’s primary allure is its brevity.

In earlier studies, workouts with intense intervals ranging in length from four minutes or even less improved aspects of health and fitness to the same or a greater extent than much longer sessions of continuous, gentler exercise, like jogging or walking.

However, the ideal length of the individual intervals remains uncertain. Several exercise scientists agree an interval should stimulate and pressure the heart, lungs and muscles, helping them to turn themselves in beneficial ways.

The studies also said that such intense workouts should not be so draining as we cannot finish the intervals or wish afterward never to work out again. Each interval should be as gruelling and tolerable.

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Edward Coyle, a professor of kinesiology and health education at the University of Texas at Austin, said that four seconds interval is a sweet spot. He and his colleagues arrived at that eye-blink number after studying fit, professional athletes.

During the tests, the athletes generated massive speed and power while pedaling specialized stationary bicycles that feature a heavy flywheel and no resistance.

The studies revealed that within about two seconds of pedaling these unique bikes, the athletes reached an all-out, maximum level of aerobic effort and power output, Coyle and his colleagues found, an effort they could maintain briefly.

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Others, not being fit professional athletes, are likely to require more time to reach maximum aerobic effort and power output during similar cycling intervals, Coyle reasoned.

The implications of the study also are cautionary. Other research, including his earlier study with students, suggests that being sedentary for long periods could have damaging effects on metabolic health, undermining the benefits from high-intensity workouts.