February: Fundamentalists

   It's the third workout that sacks you. Restarting a training program shines new light and false hope into the unvaried routine. Your legs respond with surprising stamina, as if they remember the miles they logged when you were in peak condition. The pain seems manageable. Optimism spikes and so you push (why, always, on the third workout?). The next day finds you supine on the sofa, moaning like a lovelorn walrus.

   Don't blame your legs. Your body is repenting for working beyond its aerobic base, its ability to pipe sufficient oxygen to its muscles. In the crudest sense, the term describes the capacity of your heart and lungs, since this duo of pipes and sacks constitutes your body's basic air pump.

   With weeks of training you grow new capillaries, extending the byways that allow blood to reach deep into muscle tissue so that oxygen saturates the recesses before hauling away the waste products-primarily carbon dioxide and lactic acid. Training works on a microscopic level as well; it increases the number and size of cellular mitochondria, which are the flash points where stored fuel becomes action. Think of them as several million tiny spark plugs strategically positioned around your body.

   Training, it turns out, transforms your entire being-albeit at an uneven rate. This is the essential problem. You can build leg muscles quickly, so long as you allow for plenty of rest between workouts. As soon as the muscle heals, it's stronger than before. The same is true of your heart, which, despite its life sustaining enigma, is essentially just a muscle. Increasing your lung capacity, on the other hand, is a relatively slow process, requiring weeks of huffing at a high heart rate. And the great efficiencies that come from a new latticework of capillaries and cells chock-full of mitochondria take months to acquire.

   Your aerobic base is only as good as its parts that are slowest to develop. Long, plodding workouts over months build this base. Forgo pace for distance; constantly remind yourself to bring it down a notch; add miles as penitence for your obvious lack of virtue. These workouts test the true character of a runner for their monotony alone. They are as much fun as shoveling coal. Worse, you never graduate from them. Even as speed work, hills, cross training, and adrenaline pumping exercises edge them out, you're ultimately only as fit as your aerobic base. You must always return to the long, slow run.

   The consolation is that you can devote less time to these workouts as you get stronger. They're a great place to heal wounds to the ego when you fail to compete as strongly as you'd expected or when you simply lack the enthusiasm for an afternoon of hill charges. They're the first place to turn when your running program needs an overhaul. In fact, whenever unmet need or failed ambition dogs your workouts, get back to fundamentals.