Base Miles

I have been trying to figure out what people mean when they talk about 'base miles'---and although I have no doubt that I have been building a base, I do not know what sort of base one needs before adding some a harder training regimen designed to push up my VO2 stats.

I am putting together a little roundup on the topic, here are two to start:

The short of it, a period of lower intensity training. Also known as endurance training or Long Slow Distance (LSD). The duration of the period ideal for base building varies from athlete to athlete and is dependent on a number of factors including athletic/race goals, athletic maturity (i.e. cycling age versus calendar age), fitness, hours available for training, life style (including stressors and support systems), etc. . . . if you're fit and free from injury and assuming you're racing sometime in the future, then a period of at least 6 to 8 weeks of base building is ideal. Raceplan

the goal is to build a strong aerobic foundation with miles that are run a little faster than recovery pace but slower than lactate-threshold pace, or somewhere between 60 and 75 percent of maximum heart rate. These comfortable, steady efforts are often called base miles because they form the "base" of a runner's training program, and should account for 80 to 85 percent of total weekly mileage (with the other 15 to 20 percent coming from higher-intensity training). Physiologically, base miles are important because they boost aerobic conditioning, develop slow-twitch muscle fibers, increase blood volume and glycogen storage, strengthen connective tissue, and enhance the body's ability to burn fat. Runners World