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).
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.
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.
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.
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.
