Beyond the Lactate Threshold

Put on your lab coats: It’s time for a little science lesson. As you know by this point in the book, glycogen, a form of stored carbohydrate, is your body’s preferred source of fuel for aerobic exercise. The faster you run, the more glycogen your body burns compared to how much fat it burns. Like any chemical burning process, the process of burning glycogen generates by-products. Burn paper, and you get smoke. Burn glycogen, and you get lactate. Lactate is the by-product of your body burning carbohydrates. You’ve probably heard about lactic acid. For our purposes here, that’s the same thing as lactate. Have you ever tried to sprint all-out for more than a few hundred yards? Remember how at the end of the sprint your muscles felt as though they were on fire? That’s because there was a lot of lactate circulating in your system from all the carbohydrates that were suddenly being burned to power you down the track. So much lactate was being produced that your body couldn’t clear it from your blood, so your muscles stung. Some people think that you’re damaging your muscles when you expose them to lactate.
That’s wrong. You’re always producing lactate—when you’re running easy, when you’re walking, even when you’re sitting. When you burn carbohydrates, as you almost always do, you produce lactate. Your muscles don’t ache at these low levels of effort because the rate of lactate entering your blood is equal to the rate at which it’s removed.
As you move up the intensity scale from walking to easy running, you produce more lactate, but your body also increases the rate at which it removes lactate from your blood. When you exercise above a certain intensity, however, the rate at which you produce lactate is greater than the rate at which your body can clear it.
The lactate concentration rises in your muscles and blood, and suddenly your effort feels much harder. At this point, you’ve reached your lactate threshold.
You’re probably thinking, “Thanks for the biochemistry lesson, but what does this have to do with running a 10-mile race?” Remember the basic race-training principle that I laid down last chapter: If you want to complete a race, you have to be able to cover the distance. If you also want to race the distance, then you should do workouts that improve your capacities to handle the limiting factors on your performance in that distance. For 5Ks and 10Ks, that meant doing workouts to max out your VO2 max. For 15Ks to half-marathons, that means improving your lactate threshold. Once you get past the hump of being able to cover the distance without great fatigue, the limiting factor on how fast you can run the 15K to the half-marathon is your lactate threshold. In fact, your race pace for the 15K to the half-marathon is roughly equal to your lactate threshold. Go faster than that, and you’ll start accumulating lactate in your blood. You can exceed your lactate threshold in shorter races, such as an 8K, but 15Ks to half-marathons last one to two hours for most runners, and you just can’t run that fast for that long.
To improve, then, you need to increase your lactate threshold. When you do that, your lactate threshold occurs at a higher percentage of your VO2 max. So with the right training, you can push your 15K to half-marathon pace closer to that of your 5K pace; that is, you can make better use of your basic aerobic fitness. You can run faster before you start accumulating lactate.