Gyms across America have been abuzz about HIIT, or high-intensity interval training, for quite some time. And no wonder—the workout style promises fast results with a limited time commitment. But is exercising for 20 minutes really as effective as, say, an hour-long walk (or LISS, low-intensity steady-state exercise) when it comes to burning fat, building muscle and increasing cardiovascular fitness?
So far HIIT has delivered impressive results in clinical studies. According to a study by the Department of Kinesiology at McMaster University, three sessions of low-volume HIIT (30 seconds of all-out cycling interspersed with 4 to 4 1/2 minutes of recovery) produced similar results to continuous training—but the HIIT sessions were three times shorter. For time-crunched exercisers (or people who just hate exercise), that’s pretty compelling.
Rod Dos Santos, personal trainer and owner of XPlosiveFit Fitness and Self-Defense in West Hills, CA, has found HIIT workouts to be an effective tool for his clients and not just for losing weight. “The length of a workout is not as important as intensity when it comes to weight loss, fat loss, and sustainability for health and longevity,” he says. “There’s a law of diminishing returns when it comes to how long you’re working out, whether it’s walking or lifting weights. The longer you do something, the chance of injury goes higher, especially the older you get. You can only push your body so long.”
Pushing your heart, however, can lead to benefits. In a paper from the American College of Sports Medicine, nonathletes who did one intense four-minute bout on treadmills at 90% of their maximum heart rate three times a week increased cardiorespiratory fitness by 10%.
But what about burning lots of calories? Dos Santos says the “excess post-exercise oxygen consumption” principle plays a role in his clients’ weight loss results. “Your body has to consume more oxygen to recover from a HIIT workout due to the fact your body has undergone harder exertion. Imagine you’re sprinting versus jogging or walking. When you’re done sprinting, you’re huffing and puffing. Eventually, you get your heart rate down to a point where you feel comfortable, but that doesn’t mean your body is comfortable. It’s still working overtime to bring your heart rate down.”
That idea is backed up by a study by Marshall University, which found that HIIT exercisers burned more than double the calories of moderate, steady-state exercisers an hour after both groups had stopped exercising.
If you prefer a stroll to all-out huffing and puffing, that’s totally fine. Stay with it. Low-intensity exercise gets meaningful results too, and sticking with any exercise regimen is the most important step toward fitness, period. “High-intensity interval training is not the only way to do things,” Dos Santos says. “We want you to do some yoga. We want you to go for a walk, one of the biggest benefits for a sedentary person to change their life and look better. Once they’ve started walking, they can add some high-intensity interval training if they want.”