Greg Doucette and Mike Israetel recently had a conversation about “cardio efficiency”. While THEY are not confused about the topic and understand it themselves, many people are and I thought I’d do my own take at explaining why and what others get wrong.
Greg Doucette and Mike Israetel recently had a conversation about cardio efficiency. While THEY are not confused about the topic and understand it themselves, many people are and I thought I’d do my own take at explaining why and what others get wrong.
Cycling is perhaps the best example to use here, because there, we can measure the mechanical power that you put out, the true work that you do – and this work directly translates to calories burned. If you’re putting out 200w of power, you’re burning 720 kcal/hour, it’s more or less that simple. This conversion rate essentially never changes for an individual cyclist and if it does, the change is so small that it just doesn’t matter.
However, the real world results that you get can vary hugely – because real world results are based on both your mechanical power and your technique.
For example, if you’re riding a city or mountain bike in an upright position, that 200w of power is going to allow you to go at maybe 28kmh. Ride in the hoods on a road bike, however and you now ride at nearly 32. Drops get you further, 34. Got aerobars? Now you’re doing 37kmh. If you added even more extreme scenarios – like pulling a car or drafting behind a bus, 200w might translate to 5 or 100 kmh.
This value never changes, but these values can vary wildly. This is why people get so confused about this issue – the ability to directly measure how much mechanical work you’re doing is mostly available to cyclists and on some stationary machines. In almost all other sports, you are forced to rely on indirect measurements, like speed, distance and heart rate – which are an imperfect approximation for calories burned at best and disastrously misleading at worst.
In particular, I think it’s heart-rate based calorie counters that are the most to blame for this misconception. Out of shape people start out jogging at 170 beats per minute, a couple months later they can do 140 and, given time, maybe even 110. That doesn’t mean you’re burning less calories, in spite of what your simplistic watch might tell you – it means your heart got stronger, so now it can do more work per beat.
Yes, your efficiency in terms of real world results can improve – as your experience on a bike improves and your technique gets better, you are going to be more capable of adopting those aggressive positions for a greater length of time, getting more bang for your watt. In many other sports, you can gain similar technique and efficiency improvements.
But your cardio engine doesn’t get worse. It’s not like day 1, you can do 200w and six months later, you got more efficient, so now you can only do 180. That just doesn’t happen, unless you get injured or something.
There’s a reason I’m using the word engine here – because it’s very analogous to a literal engine. The same engine in different car frames could burn the same amount of fuel, output the same power and get very different results, depending on how aerodynamic the vehicle was.
Okay, time to get our science hats on. What we’re talking about here is called gross efficiency – that is, the ratio of calories burned to your mechanical work done. Is this ratio trainable? Can it change? Well, it depends on who you choose to listen to. There are a bunch of studies that find no difference and there are a bunch of studies that do find a difference.
However… Even in those studies that do find a difference, it’s only important for scientists and extremely competitive athletes. For you, the average listener at home, the possibility of going from 19% gross efficiency to 21% gross efficiency if you train with the intensity of a competitive athlete preparing for race season just doesn’t matter.