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Steady State vs. Intervals: Explaining the Disconnect Part 1

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In this series of articles, I’ve been addressing some issues with respect to interval training versus steady state in terms of 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 Now Infamous 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.

I’d also comment that my friend Tom Venuto has recently examined the Tremblay study in some detail in his blog. Parsing the numbers differently, he concluded that the steady state exercise was actually five times as effective.

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.

As I discussed in in the Research Revivew on The Effects of Exercise Intensity and Duration on the Excess Post-Exercise Oxygen Consumption, the post-exercise calorie burn clearly can’t explain this.

What’s going on?


Muscle Gain

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.


Increased 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.

Of 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.

Read Steady State vs. Intervals: Explaining the Disconnect Part 2

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