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High-intensity interval training is any workout that alternates quick bursts of intense exertion with short intervals at a moderate pace.

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This is part of a series on aging well.

Compared to sitting all day, any exercise is better than none. But if you're determined to ward off an early death, one form of exercise, called high-intensity interval training (HIIT), may give you a leg up.

It sounds technical, but it's not. HIIT is basically any workout – on a bike, in the pool, on the pavement – that alternates quick bursts of intense exertion with short intervals at a moderate pace.

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This approach to exercise puts the brakes on important markers of aging at the cellular level, researchers say.

In a study published last month in the journal Cell Metabolism, sedentary volunteers who did high-intensity interval training showed increased activity in their mitochondria, the energy powerhouses in our cells. Mitochondria are like tiny digestive systems, converting nutrients from food into the main energy source for most of a cell's functions.

After 12 weeks of HIIT workouts, study volunteers between the ages of 18 and 30 saw a 49-per-cent boost in their mitochondrial capacity, while the 65- to 80-year-old group saw an increase of 69 per cent.

Older adults showed greater gains in their mitochondria's energy production because prior to the exercise program, "it was very low to begin with," said the study's senior author, Sreekumaran Nair, a medical doctor and diabetes researcher at the Mayo Clinic in Rochester, Minn.

Gains like these could affect a person's longevity, Nair said, noting that mitochondrial function plays an important role in endurance capacity, a measure of cardiovascular fitness.

"The higher your endurance capacity, the lower your mortality – in diabetes, cardiovascular disease, hyperlipidemia [excess fats in the blood] and hypertension."

The study included volunteers who did solely resistance training, such as weight lifting, and a group who combined moderate aerobic activity with resistance training. Compared to these two groups, volunteers who did the HIIT workouts showed the greatest recovery in mitochondrial function.

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The researchers did not evaluate how sustained high-intensity exercise, such as long-distance running, might compare with the effects of a HIIT workout, which brings the heart rate down repeatedly during moderate intervals.

The goal of the study was not to offer fitness guidelines, Nair said, but to understand the underlying mechanisms in the body's response to different forms of exercise.

But based on the findings in the study, "high intensity is a key factor for mitochondrial recovery," he said.

HIIT workouts may rejuvenate other parts of our cells as well. Telomeres, the protective caps at the ends of our chromosomes, tend to shorten with each cell division. When telomeres get too short, cells lose their ability to divide and renew the body tissues that depend on them.

But telomeres can lengthen, too. In a 2015 study, German volunteers who did six months of high-intensity interval training showed an increase in telomerase, an enzyme that replenishes telomeres. The HIIT workout, performed three times a week, consisted of a 10-minute warm-up, four alternating intervals of fast and easy running (at three minutes each), followed by a 10-minute cool-down.

If that's not enough to get you to break a sweat, consider this. In a 2016 study at McMaster University, researchers monitored sedentary men who completed a thrice-weekly cycling workout for 10 minutes at a time, of which just one minute was gruelling. After 12 weeks, the men showed similar improvements in aerobic fitness and blood-sugar control as their counterparts who had cycled at a moderate pace for 45 minutes, three times per week.

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Based on what we know so far, HIIT workouts not only help turn back the clock on aging – they're efficient, too.

The Globe's Life reporter Dave McGinn shares what he learned over the last 6 months of eating healthy and working out The Globe and Mail
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