In The Chi Marathon: The Breakthrough Natural Running Program for a Pain-Free Half Marathon and Marathon, we explain how to train aerobically so you don’t hit a wall during your next event.
I’ve come across many runners who think they need to train at their projected marathon pace on every long run in order to meet their pace goal for the actual race. You might ask, “How in the world am I going to run my projected marathon pace for the whole distance if I don’t practice running at that pace for the whole distance?” That’s a fair question, and a big one to answer. So I enlisted the help of my good friend and fellow ChiRunner Dr. Mark Cucuzzella for an explanation of the science behind aerobic training.
First of all, in order to run farther or faster, your body needs to run more efficiently. One of the important functions of the LSD run is teaching your body to burn fat as a fuel so you can run the marathon distance without bonking. In order to do that, you need to train your body to metabolize fat by running at a pace that is below your maximum aerobic capacity. By training at an aerobic pace, your body learns to burn less glycogen and more fat. Here’s an interesting fact: it takes a small amount of glycogen to metabolize fat for fuel. So if you burn through all of your glycogen stores up front (by starting too fast), you won’t have any glycogen left for when you need to access fat for fuel later on — and when you run out of glycogen, that’s when you hit the wall. Taking in glucose on the run helps, but we are most efficient in economy mode, with the majority of our fuel source coming from metabolized fat.
Aerobic training does two things: (1) it improves your oxygen exchange rate by building more extensive capillary beds in the lining of your lungs and muscle tissue, and (2) it builds more mitochondria, which are sometimes called “cellular power plants” because they produce most of the cells’ supply of a substance called ATP (adenosine triphosphate), which is a source of energy.
If you train too fast, you produce less ATP and you don’t build capillary beds that are as extensive as they can be. In scientific terms, if you run at an anaerobic pace you create only 2 molecules of ATP per molecule of glycogen, whereas when you run at an aerobic pace you can produce up to 470 molecules of ATP per fat molecule. That’s a lot of energy you’ll be missing out on if you train too fast.
I’m going to use the modern fuel-burning automobile as an analogy. There are a number of different types of engines used in cars today, and they generally fall into the categories of either speed or efficiency. Speed and economy are inversely proportional—one can’t go up without the other going down. The same rule holds true for the human body. When it comes to burning fuel we have two “engines”: one for quick accelerations and fast speeds, and a different one that kicks in when you need to run very far but not necessarily very fast.
For running shorter distances at a faster pace, your body utilizes the anaerobic system, which consumes muscle glycogen at a high glycogento-to-oxygen ratio. It’s called anaerobic because your body’s demand for oxygen outpaces its ability to fill the need, and you go into oxygen debt. To use the car analogy: car engines built for speed and high performance can do what they do because they burn a massive amount of high-octane fuel mixed with a relatively tiny amount of oxygen, creating a hotter explosion in the engine and subsequently providing more power to the wheels. It can be a fun adrenaline rush to drive fast in one of these high performance vehicles, but basically the faster you drive, the worse your gas mileage gets. It’s fun, but it doesn’t last long. Sound familiar?
On the other hand, if you need to go on a long car trip and want to save some money, you’d be smart to drive an economy car so you can get more miles for your buck. For long-distance running you’ll need to develop the fuel-efficient aerobic system. Your aerobic engine runs on oxygen, blood glucose, and metabolized fat. It’s highly efficient and can run all day on minimal added fuel. The system is called aerobic because it burns with a higher oxygen-to-fuel ratio. The physiology is complex, but the practical implications are nothing short of amazing.