What's better, running for 60 minutes at an easy-going pace or running for 30 minutes broken up into alternating chunks of sprints and jogging?
Of course, it all depends upon what your goal is. But if you want to burn fat, work your muscles harder and increase your cardiorespiratory fitness, three recent studies show interval training may be the way to go.
Unlike endurance workouts, which are comprised of moderate exercise conducted over a longer period of time, interval training, or High-Intensity Interval Training (HIIT) as it's sometimes called, is short and sweet, with high-intensity exercise mixed in with lower-intensity cool down periods.
For a new study published in the journal Cell Metabolism, scientists studied three groups of people doing high-intensity aerobic interval training, resistance training or a combination of the two for 12 weeks. All of the exercise routines improved the participants' body mass, but they also found that the HIIT group saw improvements in their muscle's mitochondria.
Why is this noteworthy? Because our mitochondria, which are responsible for producing energy for cells, become less efficient as we age. HIIT "reversed many age-related differences," the study says, in older participants' mitochondria.
An April 2016 study published in the Journal of Sports Medicine and Physical Fitness studied 39 adults for eight weeks. The volunteers were split into two groups. One group did HIIT twice a week and regular gym workouts twice a week. The other group did only regular gym workouts four times a week. While participants in both groups reduced their body fat and improved their flexibility, researchers found only the group that did HIIT improved their cardiorespiratory fitness.
A 2015 study conducted by researchers at Sweden's Karolinska Institute also looked at the health benefits of HIIT. They evaluated a group of male volunteers who alternated between pedaling a stationary bike for 30 seconds at top intensity and resting for three minutes. They completed this workout six times.
Researchers say what they found in the muscle cells of the participants reveals why HIIT workouts are so effective.
Tissues samples from the thigh muscles of the volunteers showed even after just one exercise session, the muscle cells had broken down in a way that promoted energy production to improve efficiency. Essentially, they found their muscles were reacting to the stress of the interval workout by becoming faster and stronger than before.
"During any physical training, the cell senses, ‘I have a problem here,’” Hakan Westerblad, a professor of physiology and pharmacology from the Karolinska Institute told Time magazine. “So to be better safe than sorry, they adapt so the next time they experience the intense exercise, the problem is lessened.”
And Westerblad and his colleagues found these adaptations were greater and more effective after interval training than after longer workouts. Even after just one workout, the volunteers had changes in their muscle cells that could be detected 24 hours later.
So if you're crunched for time, don't skip the workout, just dial up the intensity. You'll still get in some quality exercise and a major boost to your heart and muscle health.
Editor's note: This story was originally published in November 2015 and has been updated with more recent information.