When it comes to ultra-high-intensity exercise, more is always better, right?
Not so fast, says a new study.
Yes, we know: This may run counter to the no-holds-barred, move-till-you-want-to-vomit, workout-as-insanity school of usual HIIT workouts. But researchers are suggesting it's totally cool—in fact, even better for your cardiovascular system—if you cut your reps a bit short during super-intense interval workouts.
In a new meta review (a study of studies, so to speak), researchers at Scotland's University of Stirling examined 38 sprint interval training trials that examined the advantage of regularly performing so-called supramaximal sprints, which are ultra-high-intensity cycling sprints that require a specialized stationary bike.
When they compared the results from all those trials, the researchers found that doing fewer reps of these sprint intervals on a bike typically led to better improvements in VO2 max, a measure of your body's ability to use oxygen.
The magic number of high-intensity sprints? Two. After just two max-effort sprints, any additional sprints actually made the workout about 5% less effective.
Of course, this finding might be a little surprising if you're a regular reader of exercise science, or even just a typical CrossFit junkie. For a while, people always assumed that more reps translated into greater cardio gains. But when it comes to super-high-intensity exercises, that's not really the case.
“We found improved cardiorespiratory fitness does not suffer when people complete fewer sprint repetitions and that this may even produce better results," said lead study author Niels Vollaard, Ph.D., a specialist on oxidative stress during exercise at the University of Stirling. "The optimal number of repetitions appears to be just two, so workouts based on supramaximal sprints can be kept very short without compromising on the results.”
It's important to note this is only true for supramaximal exercise, which requires specialised exercise bikes—like an airdyne bike—that lets you hit ultra-high exercise intensities. Researchers don't know if HIIT workouts at lower intensities also benefit from a smaller number of sprint reps, but stay tuned—and, if you're feeling adventurous, test the theory out for yourself.