Glenn A. Gaesser and Siddhartha S. Angadi.

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Highlights

Traditionally, the form of exercise most commonly prescribed by clinicians is continuous moderate-to-vigorous-intensity exercise that can be sustained for 20–60 min. This is consistent with current US public health guidelines recommending that adults accumulate at least 150 min/wk of moderate-intensity physical activity or 75 min/wk of vigorous-intensity physical activity.

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The percentage of US adults meeting these minimal guidelines is extremely low. Among the many reasons for not exercising is a “perceived lack of time,” which is one of the most frequently cited barriers.

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As little as 30 min of vigorous exercise per week, within a total exercise time commitment of 75 min/wk, improved glucose control and markers of skeletal muscle metabolism in patients with type 2 diabetes.

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Over 2 wk, eight subjects completed six high-intensity interval exercise sessions,with each session consisting of 10 60-s bouts on a leg cycle ergometer that elicited 90% maximal heart rate (HRmax), interspersed with 1:00 of rest. .Albeit just a pilot study on eight subjects, the results are consistent with a number of publications within the last few years that demonstrate the benefits of HIIT.

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Low-volume HIIT typically consists of several bouts of high-intensity exercise lasting between 1 and 4 min, which elicit 85–95% of HRmax and/or VO2max, interspersed with bouts of rest or active recovery).

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Some versions of HIIT involve much shorter exercise intervals, lasting only :08, with up to 60 repetitions in a single exercise session.

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In general, HIIT involves only 8–16 min of actual “on time” for vigorous-intensity exercise, with the total workout, including warm up, cool-down, and rest/active recovery periods, requiring only 20–25 minutes.

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In the few investigations that have addressed HIIT, subjects appear to not only tolerate the higher exercise intensity, they actually prefer HIIT to the moretraditional steady-state continuous exercise. In young healthy males, it was reported that ratings of perceived “enjoyment” were higher for HIIT than for steady-state continuous exercise, despite RPE being higher for HIIT. Similarly,patients with heart failure found HIIT more motivating than traditional steady-state exercise, which was perceived as “quite boring.”

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Recent epidemiological evidence from the Norwegian HUNT study indicated that just a single weekly bout of high-intensity exercise was found to reduce the risk of cardiovascular disease in both men and women (relative risk: 0.61 and 0.49, respectively).

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With such a large percentage of the US population failing to meet even minimum physical activity guidelines, HIIT may help insufficiently active individuals overcome a major barrier to maintaining a physically active lifestyle, that of a perceived lack of time. An added bonus is that from a time-benefitperspective, HIIT may prove to be a good example where less can be more.