Runner's World Guide to Cross-Training by Matt Fitzgerald

Author:Matt Fitzgerald
Language: eng
Format: epub
Publisher: Potter/Ten Speed/Harmony/Rodale
Published: 2012-05-09T04:00:00+00:00

FOUR WAYS TO IMPROVE

Let’s employ a race car metaphor to discuss the four fundamental ways to run faster.

1. BUILD A BIGGER ENGINE. The most potent means of getting faster is to increase the rate at which your body is able to produce energy over a full race distance. The more energy your body can generate for forward motion, the faster you will be able to run throughout the race.

The most important physiological attribute underlying the capacity to produce energy at a high rate for a long period of time is aerobic capacity, or VO2 max—that is, the ability to deliver oxygen to the working muscles. There is a very strong correlation between aerobic capacity and distance-running ability. Here’s why.

Unlike a race car, which contains one engine and uses a single fuel type, the human body has two energy systems: aerobic and anaerobic. (Actually, there are three distinct anaerobic energy pathways, but since two of them combined are able to supply energy for only about 18 seconds of maximum-intensity action, we endurance athletes can more or less ignore them.) The aerobic system, used mainly for sustained actions of low-to-moderate intensity, requires oxygen to function. The anaerobic system (specifically anaerobic glycolysis), used mainly for high-intensity actions, does not involve oxygen. The aerobic system produces harmless by-products (carbon dioxide, water, and heat). The anaerobic system produces pyruvate, some of which turns into lactic acid. Lactic acid in turn breaks down into lactate and hydrogen ions that inhibit muscle contractions, cause pain, and perhaps even damage muscle tissues. This is why you can’t sprint or lift heavy weights for more than a few dozen seconds before reaching exhaustion.

Contrary to popular belief, whenever you run, at any speed, both the aerobic and anaerobic systems produce energy. When you run slowly, nearly all your energy is produced aerobically. As you speed up and burn more and more total energy, the anaerobic system is required to make larger and larger contributions. However, the faster your body is able to deliver oxygen to the working muscles, the more energy your aerobic system can produce on its own, and the faster you can go before hydrogen ions begin to build up and hasten exhaustion. Also, the aerobic system actually uses pyruvate for energy, thereby preventing lactic acid and hydrogen ions from forming in the first place. So the key to being able to produce energy at a higher rate over a full race distance is to produce more energy aerobically.

Many of the physiological variables underlying aerobic capacity can be positively affected by training. Training enlarges and strengthens the heart so that it can pump more blood and deliver more oxygen per contraction. Training also increases blood plasma volume and hemoglobin content, allowing the blood to carry more oxygen per unit volume. It activates new capillaries that deliver oxygen from the bloodstream to the muscles, and within muscle cells it increases the number of mitochondria, the structures that are the actual site of aerobic metabolism, as well as aerobic enzymes that break down fuel for energy.

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