Interval Training Doesn't Work

For years bodybuilders were eating plain chicken breasts and doing steady-state cardio to prepare for competitions. And everyone was happy. No one ever really questioned the efficacy of the mind-numbing cardio since bodybuilders had been stepping on stage completely shredded (with far fewer drugs) for decades.

Then, in the early 2000's, interval training exploded onto the scene and steady-state cardio was no longer en vogue. (Chicken breasts, however, were still unseasoned and tasteless.) I was in grad school at the time and one of my thesis committee, Dr. Martin Gibala, was doing cutting-edge research showing that intervals produced equal or even better improvements in cardiovascular fitness and performance than steady-state exercise lasting several times as long.

Other labs were cranking out research showing similar improvements in mitochondrial functions, potential for fat burning, and increased post-exercise metabolism. Finally, the 1994 study by Tremblay was brought to light and a comparison showed that interval training produced an effect that was nine times better than steady-state cardio for body composition change.

After that, the fitness world was never the same.

Of course, the new research came as no surprise to sprinters and distance runners (yes, distance runners) who had been using intervals for years. But for the fat loss community it seemed as if we'd found the ultimate in fat burning. Steady-state cardio was dropped in favor of interval training and every coach (myself included) began to use intervals in their programming.

But was it a smart decision?

Questioning the Origin

As much as I was swept up in the excitement that surrounded intervals, one thing recently started to become clear to me: None of the studies (with the exception of the Tremblay study) had actually examined the effects of intervals on fat loss in a true randomized controlled trial.

Sure, there was definitely a benefit for performance. But when it came to body composition only the mechanisms measured at the muscle level showed a likelihood of greater fat burning. Studies using real people to actually measure fat loss were limited.

I want to quickly go over three studies that represent the bulk of research on intervals and body composition and see if we can come to some sort of conclusion on the best method you can use to lose the most fat.

The Tabata Study

Since you can't really go anywhere in the fitness industry without seeing or hearing about the latest and greatest Tabata workout, I just had to include this one. All in all though, there are really only a few points I need to bring forth.

• The Tabata study does not measure fat loss. Although Tabatas were certainly effective for improving aerobic and anaerobic performance, there was no mention of fat loss in the paper at all. None.

• The steady-state group in the Tabata study performed steady-state cardio. No surprise there. But the interesting part is that the Tabata group actually performed steady-state cardio instead of Tabatas for one of the five training days. In other words, 20 percent of their training days were allocated to a different method than what they were actually testing.

• The majority of the improvements in Tabata performance happened in the first three weeks and then leveled out.

• Tabatas were done at 170% of VO2 max, which is basically balls to the wall, maximal effort training on every set.

Having read all this I came to the following conclusions: Tabatas may or may not be effective for fat loss, but it certainly wasn't measured in this study and, based on this information, there is no real reason to assume that they are better than steady-state or any other type of interval training.

In fact, you can't really draw any conclusions about the effectiveness of Tabata style intervals for anything considering that they were also using steady state exercise and the results are difficult to separate out. Finally, even if Tabatas are effective for fat loss, lifting weights to perform them likely won't enable you to exert maximal effort to reach 170% of VO2 max on every set.

If you're lifting weights, odds are that your first set is sub maximal if you're able to lift it again after the 10-second rest interval prescribed by the protocol.

Note that I'm not saying these protocols aren't difficult (anyone who's ever done a round knows exactly what I'm talking about). I'm just saying they're not "technically" Tabatas, since you're using sub-maximal weights.

The Tremblay Study

If there's a single study I've seen used to support the use of intervals for fat loss more than any other, this has got to be it. Having checked it out though, I'm sad to say that I was disappointed. Here are a few things I discovered:

• The steady-state group sessions started at 30 minutes and gradually increased to 45 minutes. Interval training sessions actually started out with the steady-state exercise around 20-25 minutes. Two different types of intervals (short and long) were added later during the 15-week study.

• The steady-state group lost only 1.1 pounds. The interval group lost 0.22 pounds. Yes, you read that right. Less than a frigging pound after 15 weeks!

• The total of the changes in skinfold measurements (taken with a caliper to assess body fat) was almost three times lower in the interval group suggesting that even though weight loss was less, body composition may have changed more.

• The interval group actually started out with higher skinfold measurements.

• There was no dietary control in this study.

You can take from this study that doing intervals or steady-state without dietary intervention will result in a maximum of one pound of weight loss. As you know, that sucks serious ass.

And even though the total skinfolds dropped more in the interval group, the trunk skinfold decrease was pretty much the same. In fact, the main reason for the difference in the skinfolds in the first place wasn't that the steady-state group didn't lose fat. The big problem was that the calf skinfold of the steady-state group actually went up which obviously affects the total. Moreover, it makes sense that the interval group (who had almost 20 percent greater skinfolds to start with) would lose more regardless of which protocol they used.

In the end, I think the body fat testing method in this study sucks. These days we use DEXA or MRI to measure body composition. And even when they did this study, hydrostatic weighing was the standard. So why'd they use caliper testing? Skinfolds can get pretty sketchy depending on your tester.

If multiple testers are used, they can be even less reliable. (This might even be responsible for the increase in calf fat seen in the steady state group, but that's total speculation.)

Ultimately, the body weight loss in this 15-week study pretty much blows donkey balls and I think this only goes to reinforce the obvious: you can't neglect your diet.

The Trapp Study

In my hunt for research comparing intervals to steady-state, I emailed my old grad school professor Dr. Martin Gibala and he admitted that the research comparing the effects of these two methods on body composition is limited. Studies with any form of dietary control are even harder to find. Fortunately he referred me to the Trapp study and I'm happy to report that there may be some support for interval training on fat loss after all. Here are the cliff notes:

• Three groups of women participated in the study. There was a control group (no exercise), steady state group (endurance exercise), and interval group (yep, they did intervals).

• All subjects had VO2 peak test, body composition tested with DEXA, three-day dietary inventory on the first and last visit, and blood tests for fasting glucose, insulin, and leptin.

• The steady-state group started at 10-20 minutes of cycling three times per week for 15 weeks. They gradually worked up to 40 minutes of exercise per session. Resistance on the bike was increased over the study.

• The interval group performed 8 seconds of sprinting followed by 12 seconds of easy pedaling on an exercise bike. Subjects performed as many repeats of this as possible until they reached 60 repeats of this sprint-rest cycle (about 20 minutes). In the beginning, many of the subjects couldn't complete the rounds, so it took a few weeks to build up to it. Resistance on the bike was increased over the course of the study. This was repeated three times per week for 15 weeks.

And the Results?

• Total estimated energy expenditure was the same for both groups after 15 weeks and no dietary differences were determined.

• As expected, VO2 peak increased in both groups

• The interval group lost weight while the control and steady state groups did not. More importantly, the interval group lost 5.5 pounds of fat while the steady-state group actually gained 0.7 pounds of fat mass.

• Interestingly, the four women in the interval group that lost the least fat were also the leanest to begin with. With these women removed the interval group actually lost an average of 8.7 pounds of fat.

• The interval group had a significant decrease in central abdominal fat whereas the other two groups actually had a slight (although statistically insignificant) gain. There was also a slight trend for the interval group to lose more fat from the legs.

• The interval group increased lean mass in the trunk while the steady-state group did not.

• Both groups decreased fasting insulin, but only the interval group was different from the control group.

• Leptin decreased in only the interval group following training as would be expected when losing body mass.

So What Does All of That Mean?

In the end, the results of this study show that interval training can lead to greater fat loss than steady state training when done in the way presented. This study also suggests that this protocol might be more effective for losing fat mass and gaining lean mass, specifically in the trunk.

Another major point to be taken from this study is that leaner people tend to lose fat slower no matter what type of protocol they're on. This brings to light the fact that the women in the interval group actually started at 35.1% body fat and the women in the steady state group started at 31.7%.

Although these differences were said not to be statistically significant, we can't ignore the fact that this may have contributed to the greater success of the interval group. You'll also note that none of the groups in this study were exceptionally lean to begin with, so this study might not be as relevant to leaner individuals.

In fact, the women who did not lose as much fat with the interval protocol were closer to a BMI of 21, so this might be more indicative of what would happen with a leaner person.

And even though there were diet records kept at the beginning and end of this study, it's possible that there were dietary differences during the 15 weeks. More specifically, high intensity training is known to suppress appetite while steady state exercise is more likely to increase appetite. This might explain why the steady state group failed to lose any fat at all when we know this method has worked for bodybuilders for years. Without quantifying this, it's hard to know whether the differences are from the training itself or from one group eating less than the other.

Of course, some might argue that interval training creates a greater "post exercise burn", but the truth is that this burn (otherwise known as EPOC) only constitutes about 13 percent of the total calories burned from interval training. So if you've burned 500 calories from the bout, a mere 75 calories might be burned in addition as a result of this effect.

My guess is that food likely played a large role since self-report isn't the most reliable form of dietary constraint. (Read: the women probably ate some doughtnuts and didn't tell anyone about it.)

The most interesting fact about this study, is the 8-second sprint followed by the 12-second light pedaling looks a lot like the Tabata protocol. However, instead of doing the protocol for 8 repeats, the subjects in this study had to do it 60 times with maximal effort to get the fat loss benefit.

So while doing "Tabatas" in the gym might technically be interval training, unless you're doing them 60 times through you're probably wasting your time.

The Bottom Line

Before I tell you what to do for the greatest fat loss, let's quickly review a few key points:

• Tabatas have NOT been studied for fat loss. But based on the last study you should be able to tell that you're going to have to put in a hell of a lot more work than you thought.

• The Tremblay study should never be referenced with regards to the success of interval training.

• Regardless of your cardiovascular protocol, diet is still number one when it comes to fat loss.

• The fatter you are, the more interval training will work for you. The leaner you are, the less effective it will be. This should really be no surprise.

• If you're going to do intervals, performing 8 seconds max effort to 12 seconds, rest three times per week seems to be the only scientifically validated method for fat loss at this time.

• Oh...and you have to do it sixty times.

So What the Hell Do I Do?

The bad news, as mentioned above is that most forms of cardio performed without any dietary change aren't really all that effective for fat loss.

The good news is that interval exercise performed with 8 seconds of max effort and 12 seconds off for a total of 60 repetitions (20 minutes) might give you an extra edge with fat loss even if you haven't changed your diet. In fact, if you're trying to put on lean mass, this might be a method you could use to mitigate fat gain.

Of course, if fat loss is the primary goal, you're smart enough to know that reducing calorie intake is necessary to maximize your results. However, the additional benefit of this protocol is that the high intensity intervals will serve as an appetite suppressant making you less hungry so you won't eat yourself into a food coma and stumble out of the local buffet like Lindsay Lohan at an after party.

So what should you do? Simply jump on a treadmill, bike, Airdyne, or local track and set the intervals in motion. To make the whole process easier, you could even pick up a Gym Boss timer to alert you to when you should stop and start each set.

This will allow you to focus on your intervals instead of watching the clock (which consequently is difficult to do when your vision is blurred from the tears associated with this protocol).

So, despite all the interval hype, it appears that only one interval protocol holds water when it comes to scientifically measured effectiveness. If you want to lose fat, go 8 seconds on and 12 seconds off for 60 rounds, and kill it! (Just don't kill yourself.)

References

Tabata, I., et al. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Med Sci Sports Exerc. 1996 Oct;28(10):1327-30.

Tremblay, A., et al. Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism. 1994 Jul;43(7):814-8.

Trapp, EG., et al. The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. International Journal of Obesity (2008) 32, 684–691.