Understanding Aerobic Capacity

The key to training to become faster at 5Ks, 8Ks, and 10Ks is to improve your aerobic capacity, or VO2 max. That’s because you run these races at very close to your aerobic capacity—an all-out 5K is run at about 95 percent of your VO2 max, a 10K at about 92 percent. To run those races better, then, you need to max out your VO2 max. The best way to do that is to do one workout each week in which you run intervals at a pace that’s roughly at your VO2 max.
But wait a minute. Didn’t I tell you early on in this book that steady, comfortable running increases your VO2 max and that it will increase by 20 to 30 percent within a year of running? Why would you need to do anything more to race a good 5K? Early on, you don’t. You’re getting fitter by leaps and bounds just by running easy. But after those initial gains, you have to work harder to keep improving. It’s like learning a new computer program—you make the greatest improvements in the beginning, when you go from complete unfamiliarity to a basic working knowledge. It’s only after more extensive experience that you learn all those little tricks of the program that allow you to make that small but significant leap from a basic user to the one in the office who every one asks for advice.
In the training schedules at the end of this chapter, I’ll have you do one speed workout each week that will focus on boosting your VO2 max by having you run your intervals at roughly that pace. In your case, I’m making them a bit faster, because I’m assuming you haven’t done systematic speed work before, so you have more room for improvement than a long-time runner. It’s important to run them as close as possible to that pace to get the greatest improvement.
In these workouts, harder isn’t necessarily better. Most runners think that if they can run a workout of three interval miles in 8:00, then running them in 7:40 will be that much more of an effective workout. But it doesn’t always work that way. In these workouts, the important thing is to work right at the limits of your VO2 max. But that’s not the same as your max.
Remember, you run 5Ks very close to your VO2 max. But obviously you can run shorter races faster; you can maintain a quicker pace for 1 mile than you can for 3.1 miles. In races shorter than 5K, a bigger percentage of your energy is supplied anaerobically, independent of the oxygen that you breathe in. So it’s possible to run faster than your VO2 max for a short distance, stop running until you catch your breath, and then run anaerobically again. Unfortunately, many ambitious runners do their speed workouts this way. They run each interval as hard as they can. When they do that, they’re definitely training hard, but they’re not training very effectively. By training faster than their VO2 max pace, their workouts are more anaerobic, so they’re training their anaerobic systems. But then they go and race 5Ks, 8Ks, and 10Ks, which rely almost entirely on their aerobic systems. In their races, they’ll often not perform up to their expectations. They’ll think, “Gee, I ran three mile intervals the other night in 7:00 each, but I could only average 7:20s in the race.” To make matters worse, they’ll then often think that this means that should train that much harder, and the next week they’ll push themselves to run their mile intervals in 6:50.
See how they’re making their workouts less and less effective the farther that they stray from doing them at their VO2 max pace? Don’t let it happen to you. Train at the right intensity, and you can pass them in the races, leaving them to wonder why you’re behind them in speed workouts, but ahead of them in races.