Hang around runners long enough and someone will bring up VO2 Max. It's an important determinant of running performance, and increasing yours is a vital part of any effective training plan.
Simply put, your VO2 Max is the measure of how much oxygen your muscles are able to use. No one is able to utilize all of the oxygen in their bloodstream. But, the more you are able to use, the faster you'll be able to run.
In order to increase your VO2 Max, you don't actually need to know what yours is. -- which is good since measuring it often involves a lot of lab equipment and a really painful testing protocol. What you do need, however, is an idea of your velocity at VO2 Max -- (v)VO2. For most people, (v)VO2 is going to be roughly the pace you can hold for 10 minutes of all-out running...
Measuring your (v)VO2 Max
As you might imagine, one way to measure (v)VO2 is to go out and run as far as you can in 10 minutes. Another approach is to simply use your current 3k or 5k race pace. Although these races don't last exactly 10 minutes, they are close enough to give you a range of paces to incorporate in your workouts. And using a race performance has the added benefit of increasing the chance that you gave an all-out effort.
Training at vVO2 (or 3k-5k pace) is going to provide the most effective stimulus for increasing your VO2 Max. Relatively long repeats (3-5 minutes in duration) at that pace will generally yield the best results. The total volume of the workout should be between 3-5 miles. And the rest interval can be in the neighborhood of 1/2 the time run to equal to the time run.
A classic VO2 Max workout is 5x1600 w/ 3 minutes rest. I've found with my athletes, though, that mile repeats are a bit more intense than I'd like a VO2 Max workout to be, and they have trouble recovering from them.
Instead, we substitute 1k repeats and shorten the rest to 2 minutes. 1k is still long enough to stimulate development, but beats them up less and allows them to have a stronger workout in the following days. But, really, any distance you enjoy will work -- or a ladder workout that mixes the distances (800, 1k, 1600, etc.).
In addition to these basic VO2 Max workouts, there are other, more race specific ways to get the same result -- especially if you're training for something other than the 3k/5k. I'll talk about those in a later post, but remember these simple guidelines and you'll be bumping up your VO2 Max in no time!