HIIT (high-intensity interval training, if you've been hiding under a fitness rock for the last year) has already been well established as the queen of all cardio. Its benefits include boosting your metabolism, burning a ton of calories in a crazy-quick amount of time (and even after the workout is over), preserving muscle, and boosting your aerobic fitness. (Read up on those and the other benefits of HIIT.)
But brand-new research shows that HIIT might have an even more exciting benefit: keeping you young. Scientists analyzed three groups of people exercising via HIIT, resistance training, or a combination of strength/cardio over the course of 12 weeks in a new study published in Cell Metabolism. The researchers found that all three types of exercise improved their lean body mass—but only the people doing HIIT had improvements in 1) aerobic capacity and 2) exercise capacity of their muscles' mitochondria (the powerhouses in your muscle cells). As you age, mitochondria become less efficient, which is linked to insulin resistance and lower cardiorespiratory fitness, according to the researchers. The HIIT regimen actually appeared to reverse the age-related decline in mitochondrial function and proteins needed for muscle building.
Based on current research, there's no substitute for exercise when it comes to delaying the aging process, said study senior author Sreekumaran Nair, M.D., in a release. "These things we are seeing cannot be done by any medicine."
The 36 men and 36 women participating in the study fell into two groups: young (18–30 years) or older (65–80 years). In the HIIT-only group, people did cycling intervals three days/week and walked on the treadmill two days/week; the resistance training group performed weighted upper and lower body exercises two days/week; the combined group did five days/week of moderate-intensity cycling and four days/week of strength training (with fewer repetitions than the resistance training-only group). The researchers took biopsies of their thigh muscles and compared the cells to samples from sedentary volunteers.
In both young and older adults, HIIT training increased aerobic capacity, insulin sensitivity (which reduces diabetes risk), mitochondrial function, lean muscle mass, and muscle strength. Adults who only did resistance training increased insulin sensitivity and lean muscle mass, but not aerobic capacity or mitochondrial function. The group who did both types of exercise had modest gains in lean muscle mass and aerobic capacity, as well as modest gains in insulin sensitivity in young people.
The most exciting finding, though, is that HIIT increased mitochondrial function in young people by about 49 percent and in older adults by 69 percent—effectively "catching up" to the cellular function of the young 'uns. (Bonus benefit: Science says that hard exercise is actually more fun.) In the combined training group, however, only the young people saw an increase (38 percent) in this type of cellular function. And that's not the only cellular-level wizardry that happens with exercise. The researchers found evidence that exercise encourages cells to boost mitochondrial proteins and proteins responsible for muscle growth, as well as increase muscle protein content. (This is big because muscles cells don't reproduce easily, according to the researchers.)
The overall takeaway: Exercise is good for your body (duh), and to get the biggest anti-aging cellular boost, HIIT is the way to go. However, because you lose important muscle strength with age, a combo of HIIT and strength training might be the golden ticket to staying healthy into your golden years, says Nair. (Better yet, pick a HIIT routine that uses weights, like this dumbbell HIIT workout that maximizes your afterburn.)