But even the researcher behind a new study that compared the two techniques in a head-to-head contest says he continues to be amazed at what you can accomplish with interval training.
For the study, men who had previously been inactive exercised on stationary bikes 3 times a week for 12 weeks.
Half of those men did a 10-minute interval workout that included 3 sets of 20-second sprints separated by two minutes of recovery at an easy pace. They also did a 2-minute warm-up and 3-minute cool-down of easy pedalling.
The participants assigned to the traditional cardio group had to log five times the minutes in the gym: for each workout, they cycled at a steady, moderate pace for 45 minutes, with a warm-up and a cool-down, for a total duration of 50 minutes.
At the end of 12 weeks, both groups increased their VO2 max—a measure of cardiorespiratory fitness—by 19 per cent, and significantly improved their insulin sensitivity and muscle health.
They both lost a similar amount of fat, too, reducing their body fat by about 2 per cent.
How is that possible?
It appears that you can trigger the same physical adaptations to your cardiovascular system and muscles through short bursts of intense activity that you can with longer, easier bouts of exercise, says study author Dr Martin Gibala, a professor of kinesiology at McMaster University.
And the similarity in fat loss can be credited to the afterburn effect, Gibala says.
Even though you may burn more kilojoules during a 50-minute moderate workout than you would during a 10-minute interval session, your 'joule burn as you recover from your workout will be greater after sprint intervals.
That’s because intense exercise is more metabolically demanding on your body, Gibala says. After your workout, you burn more kilojoules restoring the energy that was depleted during the sprints.
Ten-minute workouts won’t cut it for everyone, of course.
For one thing, if your main goal is to lose fat, it’s worth noting that the fat loss for these subjects was modest: on average, they went from 30 to 28 per cent body fat over three months.
That’s because even with the afterburn effect, Gibala estimates that the average person would only burn about 150 calories with the 10-minute interval workout. (Plus, there were no restrictions on how much the subjects ate, which is obviously a crucial part of the fat-loss equation.)
For a better kilojoule-burning workout, you could try stacking two or three of these 10-minute sessions back to back. The harder and longer you exercise, especially during your sprints, the more 'joules you’ll burn, Gibala says.
And if you’re already an elite athlete, you may need a harder, longer interval protocol to improve your VO2 max.
But the bottom line is this: no matter what shape you’re in, interval training can help you take your fitness to the next level, Gibala says.
And more importantly, it can give you the flexibility to fit an extremely effective workout into a jam-packed day.
“Even if you only have 10 or 15 minutes, you don’t have to blow off your workout,” Gibala says.