PUBLISHED 04/01/2006
A lot of runners tend to compartmentalize their training. You've got your distance days; you've got your speed days. Like the estranged couple who are both still your friends, distance and speed are easier to deal with when they're apart. But there are the inevitable moments when the couple comes together for, say, a wedding, graduation--or race day. To be competitive, you're going to want your distance and speed training, each with their unique attributes, to be perfectly compatible.
Your distance runs, of course, produce aerobic gains, including increased blood volume and capillarization, enhanced mitochondrial density and size, and improved slow-twitch fiber development. Running at a pace where your heart's working at 60 to 80 percent of its maximum primes the body's ability to store glycogen (keeping us from bonking in future marathons) and to use fat as a fuel source (managing weight).
Once you step over about 80 percent of your maximum heart rate, you're training for speed. Embrace it to reach your full potential as a runner. As you move up in intensity, you encounter your lactate threshold at 80 to 87 percent of maximum heart rate. Working in this range develops fast- and slow-twitch muscle fibers and increases heart-chamber size, stroke volume, and VO2 max. Lactate-threshold training--tempo runs, cruise intervals, and marathon-pace runs--lets you run faster, comfortably, because you're producing less lactic acid.
