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The High Intensity Cardio Debate

Studies break down HIIT effectiveness.
Interval training for muscle growth
Andrew Cutraro

In today’s gym, the wildly popular and hyperintense cardio workout has many faces: that guy sprinting full-tilt on the treadmill, the girl whipping ropes into the floor like a child throwing a tantrum. It also encompasses kettlebell swings, kickboxing classes, burpees—and basically anything else that involves short bursts of brutally intense exercise followed by periods of lighter activity or rest.

High-Intensity Interval Training (HIIT) has been the leading movement in cardiovascular exercise for fat loss and conditioning for more than a decade—ranked No. 1, in fact, on the American College of Sports Medicine’s survey of fitness trends for 2014. Fueled by claims of faster fat loss, shorter workouts, and less monotony (along with exclamations such as “It kicked my ass” or “Made me puke”), HIIT has largely supplanted traditional aerobic training—of the just-go-out-and-jog variety—as the preferred conditioning method of gym-goers everywhere. But old fashioned roadwork, the kind that Muhammad Ali and dozens of other champion athletes utilized, isn’t obsolete. In fact, it may actually be the more important style of cardio exercise for anyone looking to be in better, more well-rounded shape.

“The biggest reason aerobic training has fallen out of favor in the fitness industry is the flashy headlines,” says Joel Jamieson, author of Ultimate MMA Conditioning (available at 8weeksout .com) and strength coach to MMA fighters, pro football players, and other athletes. “We like the idea of being able to lose weight in four minutes versus 40 minutes, but it’s not the right approach.” He points out that the research HIIT enthusiasts frequently cite for support is often very short-term and flawed.

In 1996, a study was published that has perhaps done more to buoy the current HIIT movement than any other. Japanese researchers, led by Izumi Tabata, published the now-famous Tabata study, which showed that well-trained young men improved anaerobic endurance more in six weeks with interval training than a control group did by performing aerobic exercise. The experimental group performed intervals for only four minutes at a blistering intensity—20 seconds on, 10 seconds off. Because of the remarkably short workout time, the study has been hailed as proof that HIIT is vastly more efficient than aerobic training. However, the findings have since been greatly exaggerated to suit the HIIT agenda, and experts argue that the study simply doesn’t apply to the regular gym-goer.

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For one thing, results for the interval group began to level off after the third week. For another, the interval group performed some aerobic training (30 minutes’ worth) in addition to the intervals, so it wasn’t a pure test of HIIT. Furthermore, the “moderately trained” experimental group performed its intervals at a staggering 170% of VO2 max, the maximum amount of oxygen the body can use during exercise. Considering that 100% of VO2 max is enough to exhaust most people, you get a sense of just how fit these “moderate” subjects were.

Now consider a 2008 study from Medicine & Science in Sports & Exercise, in which eight obese men trained for four weeks at a moderate, constant pace (also known as “steady state”). Data were collected, and the men then performed another four weeks of intense interval training. On both programs, the subjects’ diets were set to avoid weight loss to allow for a pure test of the exercise protocols.

The workout length on both programs was the same, and so was the subjects’ average energy expenditure and body composition (remember, they never cut calories from the diet). Still, the men burned more fat on the steady-state protocol than with the intervals. In fact, the aerobic training yielded a jump of 44% in the amount of fat burned during exercise, while the intervals caused zero.

So what does all this science really mean? Well, two things. The main one is that cardio, whether steady state or intervals, doesn’t do much for fat loss. (Though the subjects burned more calories from fat during aerobic exercise, they didn’t lose weight overall.) And second, interval training isn’t necessarily any more effective than aerobic work, in any time frame. In fact, to truly maximize your performance and minimize fat, you need to be doing a combination of the two.

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