Understanding Endurance – Mario Fares (Part 1)

Aerobic and Anaerobic metabolism:

Within athletics, endurance is the maximum sustainable work rate an athlete can maintain for the duration of an event before fatigue makes a reduction of the work rate. Usually, the reduction in the work rate is caused by your body’s inability to meet the energy demands of the exercise, by a depletion or an accumulation of certain metabolites, or by a reduced motor nerve signal.

What powers the muscular work?

ATP! “Adenosine Triphosphates” is the short-term energy storage molecule used by every cell in your body. The energy released when ATP molecule’s chemical bonds are broken is what powers muscular contractions. The ATP supply, specifically its rate of production, becomes the limiter of your endurance; endurance athletes need to not only improve the rate of turnover of ATP, but also to ensure that this rate can be sustained for as long as needed for the specific event.

The body relies on two metabolic pathways to create ATP, Aerobic and Anaerobic metabolism:

• Aerobic Metabolism:
  This process relies on oxygen to function and uses fats to produce ATP. It produces seventeen times more than the anaerobic system can produce but it is more complex and has a slower process.
• Anaerobic Metabolism:
  This process relies on carbohydrates, sugars are converted to glucose by the liver and directly transferred to the muscles or stored in the liver for later use. This system does not require oxygen to perform. The end product of this metabolism is a molecule called Pyruvate and two ATP molecules. The latter are produced faster and used when the demands on the ATP become higher such as during high-intensity exercises.
  Pyruvate can take two roads after its production; it can be reused and produce thirty-six more ATP molecules or it can be converted into lactic acid, which plays the main role in determining the athlete’s performance. When lactic acid molecules are formed, they dissociate into lactate molecules and hydrogen ions. The accumulation of these metabolites causes muscular fatigue and decreases the pace.
  The aerobic metabolism of fats produces no lactate, which makes it more desirable to fuel endurance sports. At lower intensities, Pyruvate production is minimal to the point that most of it can go to the aerobic pathway and produce more ATP molecules. During this process, the athlete is operating below his aerobic capacity. When the intensity increases, the body switches to the anaerobic pathway and lactate and Hydrogen ions will start to accumulate.

Inspired by the Philosophy of  The Uphill Athletes

Source: Training for the Uphill Athlete: A Manual for Mountain Runners and Ski Mountaineers.

-by Mario Fares, Certified Personal Trainer