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Steady State vs. HIIT: Explaining The Disconnect

In this series of articles, I’ve been addressing some issues relating to the debate over steady state and interval training for fat loss.    In the last two posts, hopefully I’ve made the point that a lot of what the pro-interval crowd is resting the benefits of interval training on (namely EPOC, which is the post-exercise calorie burn) is a whole lot of nothing.

With any realistic amount of intervals, not only does the total calorie burn of the workout itself pale compared to longer moderate intensity steady state sessions, the EPOC simply doesn’t amount to anything. Certainly not enough to explain the rather rabid and myopic recommendation of that form of training.

Yet we seem to have something of a real-world problem, there is an apparent disconnect with the physiology that I’ve (so-far) looked at and the results of research (or the real world), many of which are showing greater fat loss with the interval versus steady state exercise mode. In the next two blog posts (this one and Friday’s), I want to look at some of those issues in some detail.

The Original Tremblay Study

So far as I can tell, one of the first studies to compare fat loss for interval versus steady state training was done by Tremblay back in the mid-90’s. I’m actually fairly sure I was the first one to report this study, in my first book The Ketogenic Diet.

In that study, subjects either followed a fairly standard steady state cardio training program or worked into intervals (after a roughly 4 week base period) over the length of the study. The interval group lost more fat and had a larger drop in skinfolds despite burning significantly fewer calories than the steady state group and training for much less total time.

I’d note that this is where the claim of “Nine times greater fat loss” is coming from. The researchers took the difference in fat loss (three times as much drop in skinfolds) and divided by the total time investment (roughly 1/3rd as long) to get 9 times as much.

Pay close attention to the changes in weight in the chart in Tom’s blog: the interval group lost a whopping 0.5 kg (1.1 lbs) over 20 weeks, the steady state group 0.1 kg (0.2 lb). Not as impressive when you look at it that way, unless you consider a 1 pound loss over 20 weeks good.

Other more recent studies, comparing various interval sessions to steady state have often found at least qualitatively similar results, at least in the context of the study (which is almost always untrained individuals who are not doing weight training and not controlling diet), intervals typically generate more fat loss.

But as I’ve discussed,  the calorie burn after exercise can’t possibly explain this.

What’s going on?

HIIT Increases Muscle Mass

Given that the subjects are typically beginners, it’s possible (although generally unstudied) that the intervals stimulated some muscle gains. The often low total weight loss (despite measurable fat loss) would tend to support that idea, the calories being used for muscle synthesis might add to the effective deficit.

However, what happens if you’ve got someone who is lifting weights as well? What if you have someone who is advanced, they sure as shit won’t be gaining muscle from bike intervals. So even if this is true, it will only hold for rank beginners doing nothing but interval work in the first place.

I’d note that pretty much every study of interval training points out that the intensities used are not sustainable by beginning exercisers in the first place. This has long been one of those ironies surrounding exercise; typically the only people able to burn lots of calories with exercise are trained athletes. And they usually don’t need to lose fat.

HIIT Increases Fat Oxidation

A follow-up study by Tremblay actually showed that the interval group saw a significant increase in the enzymes responsible for fat oxidation; surprisingly this effect happened fairly quickly. Given that obese individuals often have a defect in fat oxidation, this could be profoundly beneficial.

This effect is assuredly mediated through both effects on gene expression as well as the glycogen depletion that occurs with high intensity activities; as I’ve mentioned in all of my books glycogen depletion itself enhances full body fat oxidation. If you increase the body’s utilization of fat for the other 23 hours of the day you aren’t exercising, that’s a good thing from a fat loss perspective. Coupled with a calorie reduced and controlled diet, enhancing fatty acid oxidation during the day goes a long way towards explaining enhanced fat loss.

I’d note that steady state cardio is known to cause an increase in fat oxidizing enzymes as well although it typically takes longer than two weeks. I’d also make the same point as above, while the above certainly holds true for intervals versus steady state being done in isolation, what happens if weight training is added.

Or if diet control is placed on the body.  If I deplete someone’s glycogen stores with a combination of full body weight training and carbohydrate restriction (as in the Ultimate Diet 2.0), I can get impressive full body increases in fat oxidation too. In about 3 days.

The Hormonal Response to HIIT

The hormonal response to any kind of high-intensity training is significantly different than in response to low-intensity training. While low intensity training typically only releases noradrenaline (from the nerve terminals) with only small amounts of adrenaline (from the adrenal medulla), high-intensity exercise releases both adrenaline/noradrenaline in large amounts.

For various reasons, all of which are discussed in some detail in The Stubborn Fat Solution, that hormonal response can be beneficial to fat loss. Quite in fact, in that book, I use intervals for specifically that reason in two of the stubborn fat protocols.

In addition to potentially impacting on fat mobilization (lipolysis), this hormonal response can have one other major effect that is probably a major cause of the results in many of the studies being cited by the pro-interval group. That’s that high intensity exercise often blunts hunger.

Blunted Hunger and Appetite from HIIT

If there is a single glaring flaw in nearly all of the research that is being used either in support of intervals or to tear down steady state cardio, it’s that diet is uncontrolled. This is important for two reasons, one physiological and one practical.

The practical one should be pretty damn obvious: anybody who is trying to lose fat without paying attention to their diet has it ass-backwards (for context, one of the most rabid pro-interval gurus has ‘Correct Nutrition’ as the #1 bit of importance in his Fat-loss Heirarchy). He’s assuming that diet is fixed, and then using research that is not controlling diet at all.

The other issue is a physiological one, having to do with how exercise can impact on appetite. Now, this could be an entire blog post (or series in its own right) as there are myriad physiological and psychological ways that training can impact on appetite (sometimes exercise decreases hunger, sometimes it increases it).

However, at least one data point shows rather clearly that high intensity activity tends to blunt hunger more than low-intensity activity.

Quite in fact, in one of the studies currently being used to claim that ‘Steady state cardio makes you fatter’ (the steady state group had a 0.5 kg fat gain in visceral fat compared to a 0.5 kg fat loss in the interval group), the researchers explicitly state:

“However, our estimates of energy expenditure and intake lack sufficient precision to comfortably conclude that energy balance was unaffected in the HIIE condition. Thus, it is feasible that the change in FM that occurred in HIIE may have been influenced by unreported changes in diet. Indeed, HIIE- induced suppressed diet intake may be one of a number of possible factors underlying the fat loss effect of HIIE.11 For example, HIIE may have suppressed appetite or decreased attraction for energy-dense foods.24,25.”

Meaning that the interval group may have lost fat because the exercise may have made them eat less.

While a huge benefit if someone isn’t controlling calories has no real relevance if they are. I’d also note that the total fat loss in that specific study wasn’t much, a whopping 1.5 kg (3.3 lbs) over 15 weeks. The Rapid Fat Loss Handbook can take that much fat off of a person in ONE WEEK.

Tangential question with a tone that moves beyond snarky and to outright accusation: how come the pro-interval gurus who trot out these studies don’t ever mention these specifics when they claim that intervals are superior to steady state cardio? That the intervals may have simple worked because subjects ate less, or that the actual real-world fat loss amounted to jack shit in the first place?

Making People Train Intensely for Once

Ok, this one isn’t addressed in the research but it’s still important to results.

Let’s face facts, most people train like wimps. I don’t care how hard they claim to work, I’ve spent damn near 20 years in commercial gyms and the simple fact is that most don’t.

Go look at the average person on the treadmill, odds are they aren’t even breaking a sweat or doing anything beyond watching tv and talking on their cell phone. And while my comparison on Saturday was intervals to a moderate aerobic sessions (where I can easily burn 10 cal/min), the average person may be burning closer to 5 cal/min during ‘fat-burning’ cardio. Or 150 calories over a 30 minute pissant steady state session. Under those conditions, a 20 minute interval session (which may burn 200+ calories) actually does win out from a simple energy balance perspective, in addition to any other benefits discussed above.

If there’s one thing that the whole interval training fad has done, it’s to get people to actually work somewhat out of their comfort zone. But to a great degree, this has less to do with steady state cardio as a modality and more about how it’s used. Fine, people usually do steady state cardio at irrelevant intensities. No argument here. But that has nothing to do with steady state and more to do with the fact that people are

  • Being given shitty advice (fat burning zone, bro)
  • Lazy

So, yes, if telling them that intervals is going to MELT THE FAT OFF OF THEM actually gets them to work hard, that’s a benefit. I’d also note in this context that this can backfire. People who are too wimpy to suffer aren’t going to do intervals effectively and will probably end up getting LESS out of an interval workout (that they half-ass) than a properly done steady state cardio session (which they’ll also half-ass).

And of course none of this really gets back to the question I posed on Saturday regarding how often I can or should do intervals compared to how often I can or should do steady state. Which is what my next article will discuss.

Now let’s take a quick look at the topic of Exercise Efficiency

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