This article appeared in Running Times Magazine in 2006.
One of the key decisions you make as a runner is how to optimize the effectiveness of your limited training time.
When Running Times readers write in asking whether to do more intervals, increase their mileage, run hill repeats, etc., my answers always go back to the physiological requirements of each runner’s goal race. Your aerobic system provides about 95 percent of the energy used in a 5K race and more than 99 percent of the energy for a marathon, so it is logical to fully develop that system before focusing your effort elsewhere. Let’s "go back to basics" and examine the benefits of aerobic base training and how to develop a big aerobic base.
What I mean by a big aerobic base is the sum total of cardiovascular adaptations gained by putting in relatively high mileage for a prolonged period of time. This concept was advanced by Arthur Lydiard in the early 1960s, when New Zealand’s Peter Snell and Murray Halberg won Olympic titles and broke world records with at-the-time unconventional base training of 100-plus mile weeks. Forty years later, the top American runners, such as Alan Culpepper, Deena Kastor, and Meb Keflezighi, and world champions such as Paula Radcliffe and Kenenisa Bekele, devote a portion of the year to developing huge aerobic foundations that will serve them well during their racing seasons. They know that their aerobic base allows them to gain the full benefits of their higher intensity training later in the year.
How does a big aerobic base improve your running performance?
Your cardiovascular system consists of a series of steps that bring oxygen from your lungs to the mitochondria in your muscle fibers. Aerobic base training produces a wide range of positive adaptations that optimize your cardiovascular system and improve your ability to produce energy aerobically.
One of the most important adaptations to aerobic base training is an increase in the number of capillaries surrounding the muscle fibers. Capillaries are the transportation system for your muscle fibers, bringing oxygen and fuels in and waste products, such as carbon dioxide, out. By increasing the number of capillaries per muscle fiber, base training improves the ability to provide oxygen to the individual muscle fibers.
Other important adaptations to aerobic base training increase the ability of your muscle fibers to use that oxygen to produce energy aerobically. Mitochondria are your muscles’ aerobic energy factories. Base training increases the number and size of the mitochondria in your muscle fibers and also improves the efficiency of the mitochondria by increasing the activity of aerobic enzymes. These adaptations reduce your lactate levels and allow your muscles to use more fat and less carbohydrate to run at a given speed. A big aerobic base helps improve your ability to recover from training and enables you to handle more high-intensity training such as tempo runs, VO2-max intervals, and speed work.
How do you develop a big aerobic base?
Slowly and persistently. The key is to accumulate mileage over the course of months and years. Most distance runners should include two blocks of base training in their annual running plan. The minimum period required to obtain a significant improvement in your aerobic base is about six to eight weeks.
If you live in a part of the U.S. where you can train consistently through the winter, then starting aerobic base building in January provides about 12 weeks of solid training before the spring racing season kicks in. Similarly, if you can stand the heat, the relatively quiet racing months of July and August can be a good time for six to eight weeks of base work. With two solid blocks of base training per year, on top of your otherwise "normal" mileage, your aerobic base should build steadily from year to year.
How much and how quickly you should try to increase your mileage depends on your propensity for injury. Although you can increase your mileage dramatically over several years, increasing too much at once is almost certain to leave you injured. As a general guideline, most runners can handle an increase in mileage of 10 to 15 percent every two to three weeks. For example, if you have been running 40 miles per week, you would increase to 44–46 miles for two to three weeks before increasing your mileage again. No rule of thumb works for every runner, however, so you need to pay close attention to your body’s feedback to find the optimal formula.
During your base training, you should avoid VO2-max sessions and speed work and slightly reduce the overall intensity of your training. By backing off the intensity, you can increase your mileage without increasing the overall strain of training. When you are building up your mileage, it is particularly important to train on soft surfaces to reduce the accumulated jarring on your body, and to be sure that your running shoes are in good repair.
Aerobic cross-training, such as cycling, swimming, elliptical training, and deep-water running can contribute to your aerobic base with less risk of injury than further increasing your mileage. The more similar the cross-training activity is to running, the greater the crossover effects will be. If you have a history of injury or live where the winter (or summer) is not conducive to high mileage training, then cross-training can be a worthwhile component of your aerobic base training.
Two-time Olympian Pete Pfitzinger is an exercise physiologist.
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