A while ago, I became aware of a new buzzword doing the rounds on certain fitness web sites. These come and go, and I usually ignore them, but this one has stuck around for longer than usual.
It sounds great. HIIT (high-intensity interval training) is supposed to increase your fitness and burn your body fat faster than other fitness methods. For some reason, some of the proponents have started taking pot-shots at endurance athletes, especially runners, for how wrong their training is. What is in it?
HIIT works the following way: After a warm-up period, you perform a series of short sessions at maximum effort separated by moderate effort recovery periods. A typical workout would be 8-second stationary bike sprints followed by 12-second passive recoveries (those sessions can be done on various types of equipment, including running on the surface of your choice, of course). The main selling point of a program like this is that you keep burning extra calories even after the workout has ended, due to a phenomenon known as excess post-exercise oxygen consumption (EPOC). Your body will be at a higher level of metabolic rate for up to 24 hours after exercise, which can burn 6-15% additional calories. As an example, if you burn 500 calories during your workout, you can expect to burn up 75 calories in the hours following the exercise “for free”. A study conducted at the University of New South Wales, Australia, found that women lost an average of 10.5 percent of their fat mass after 15 weeks on a three-times-a-week program.
Losing more than 10 percent of your body fat after exercising for only 20 minutes, 3 days a week sounds great, doesn’t it?
Well, there are a few drawbacks.
You can’t just hop on a bike and start churning out maximum effort. A proper warm-up and cool-down session will increase your exercise time from 20 minutes to close to an hour—in which case, you don’t save any time compared to normal running training.
Even though 8 seconds-worth of high intensity exercise doesn’t sound like much, a 20-minute workout like this would include 60 all-out sprints, which makes this a very, very hard workout. The promise of “easy” fat-loss is false. You have to work very hard for your gains. People who are selling a program like this to a couch potato promising easy gains are basically lying through their teeth. Anyone not used to exercise will simply find the training too hard.
If you study the training of serious distance runners, you’ll see that they include interval workouts that can look very much like those HIIT sessions. All the way back in the ’50s, legendary New Zealand coach Arthur Lydiard prescribed his athletes workouts like a sequence of 50 meters sprint/50 meters float, which is remarkably similar to a 8 seconds/12 seconds HIIT workout. Lydiard called them “sharpeners”, and he used them to fine-tune his runners’ peak fitness—not as the basis for the training program. Maybe he should have thought of a snappier name and created an ad-laden website instead.
If something sounds too good to be true, it usually is. You don’t turn into a super athlete by training for just 60 minutes per week. Hard training sessions like the ones prescribed by HIIT certainly have their place, such as in Lydiard’s program, and they do provide a very good stimulus to your body. However, the claim that they can replace any other form of training is simply false.