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Explaining Exercise Efficiency

Continuing with the topic of steady state vs. interval training, I want to look at the topic of exercise efficiency.  This is an aspect of exercise physiology that is misunderstood by most who write about it.  And sadly this misunderstanding is what leads them to draw some very bad conclusions.

What is Exercise Efficiency?

You can consider this article a sort of side-trip about the whole issue of intervals versus steady state cardio that I’ve been discussing in the previous articles. I’ve mentioned exercise efficiency briefly in a couple of posts but want to make some more detailed comments before continuing on with the series..

One of the common arguments against steady state cardio is something akin to ‘Steady state is useless because you become more efficient at it and burn less calories doing it.’

I’ve already addressed part of why this argument is stupid but want to go into a bit more detail.

The simple fact is that you get more efficient at anything you do regularly. This is true of weight training and interval training. And what do you do when that happens? You increase the workload (e.g. add weight to the bar, try to go faster in your sport, use a higher intensity for your intervals). Duh.

Yet somehow that same logic seemingly can’t be applied to steady state cardio, at least not according to gurus with an interval program to sell.

Somehow, even though you get better at it (assuming that this does significantly impact on calorie burn, which I’ll address next), you can’t ever work harder.

That is to say say I start walking at 3.5mph on a treadmill. Say that six weeks later I’ve become more efficient and am burning less calories. Are the anti-steady state people seriously suggesting that I can’t simply raise the workload to say 3.8 mph (or 3.5 mph on a 1.5% incline) to burn more calories (to offset any increase in efficiency)?

Yes, that does seem to be what they’re saying. So while it goes without saying that they would suggest adding weight to the bar when things get lighter, or increasing the intensity of intervals when they get harder, this somehow can’t be applied to steady state cardio. Can you understand why I have such a bug up my ass about this topic and the stupid arguments involved? It’s because they make absolutely zero fucking sense.

But I digress.

Do Changes in Exercise Efficiency Matter?

A bigger question is whether any of the above actually makes a shit’s worth of difference for the average trainee. That is, does efficiency really improve so drastically as to radically reduce caloric expenditure during steady state (some people seem to have this implied idea that you’ll be burning like half as many calories due to improved efficiency, or whatever)?

The short answer is no.

The long answer follows:

First I should probably define efficiency in the sense it’s being used here. The key thing to realize in looking at this is that most of the energy that you expend on any activity is lost as heat, only some percentage of it actually goes to producing actual work.

I mentioned in a previous blog post that, for cycling, this number ranges from about 20% (only 1/5th of the amount of energy you burn actually goes to power production) to 25% (1/4 of the total amount of energy burned goes to work production). Essentially efficiency is a measure of how much external work you get for a certain input of energy.

Of course, from a performance point of view, higher efficiencies are better, the more mechanical output I get for a certain amount of energy input, the faster I will go (on the bike, running, etc).

Exercise Efficiency and Calorie Burn

Now, the next question to look at is how much caloric expenditure (e.g. to cover a certain distance) varies for that range of efficiencies. Let’s say I ride my bike and generate a total power output of 420 kj (I’m picking this odd value to make the math simpler). To convert this to calories, I divide by 4.2 so that’s 100 calories. But only that only represents some percentage of the total I burned because only 20-25% of what I burned calorically went into the actual power output that my Power meter measured.

So to calculate it back out, I can divide by 0.2 for 20% efficiency or 0.25 for 25% efficiency. I’m going to use the extremes to save a bunch of calculations and look at what the maximum realistic change might actually be.

100 calories /0.2 = 500 calories burned

100 calories /0.25 = 400 calories burned

No doubt, I burn fewer calories if I’m more efficient, about 20% less comparing the lowest efficiency to the highest efficiency. So for every 1% increase in efficiency, I burn 4% fewer calories at the same workload.

How Quickly Does Exercise Efficiency Change?

But here’s the next question, how much training does it take for me to go from a 20% efficiency to a 25% efficiency? Or even to increase my efficiency by 1%?

The short answer is: essentially forever.

The longer answer is: ok, not exactly forever but it’s a time frame that is utterly irrelevant to the general population.

To make my point, I’m going to pull a data point from a study of arguably the most dominant cyclist to yet live: Lance Armstrong.

Tracked over approximately 7 years of training, Lance improved his efficiency by a whopping 8%. Or roughly 1% PER YEAR. And, to quote the paper directly:

“It is hypothesized that the improved muscular efficiency probably reflects changes in muscle myosin type stimulated from years of training intensely for 3-6 h on most days.”

Read that closely, three to six hours of cycling per day damn near EVERY DAY to get a 1% efficiency increase PER YEAR.

And yet, somehow, folks think that walking on the treadmill a few times per week is going to ramp up their efficiency such that they are burning massively less calories during their workouts after a few weeks.

Note: A recent controversy has erupted over the paper I cited above. There are now accusations that Coyle mis-analyzed the data; the re-intrepretation suggests that Lance actually did not improve his efficiency much at all. Which is yet another nail in the coffin of the entire argument: if Lance Armstrong, cycling 6 hours per day damn near daily for years on end isn’t becoming more efficient, someone walking on the treadmill a few times per week damn sure isn’t either.

Sorry folks, it doesn’t work that way. There’s a reason that endurance athletes train damn near daily for years on end to reach their ultimate genetic limit of performance. After VO2 max peaks and lactate threshold peaks, the only way to get better is with efficiency improvements. And it takes years of grinding effort to improve this by even a small amount.

Exercise Efficiency vs. Getting Fitter

But you say, what’s happening when, after a few weeks, it’s suddenly easier to do my workouts?

That’s not efficiency, that’s called improving fitness.

And, as above, when that happens you have to increase the workload.

When 100 lbs on the bar is too light, you go to 110 lbs.

When 200 watts during intervals is too easy, you go to 220 watts.

And when 3.5 mph on the treadmill becomes easier, you raise the speed, incline or both.

Yet every pro-interval guru who would tell you do the first and second, seem to feel that it’s impossible to do the third.

Note: For folks coming in late, let me make it clear again that I am not trying to make an argument for steady state or against interval training (as both have their roles to play), I’m simply trying to point out some of the more idiotic arguments being made by the pro-interval camp to try and discredit steady state cardio as a useful modality.

Next up, I want to look at Metabolic Adaptations to Short-Term High-Intensity Interval Training

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