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A Letter to Mrs. McCarthy*-Part Two

Posted by Filed Under: Learn to Run

This is a three-part essay I composed for an acquaintance who had met me for lunch recently to discuss “how to run.” Over the next few days after the lunch, I sent her the attached. Read part one here.

Dear Mrs. McCarthy,

learn-to-run.jpgThere is one, and only one, major component to a runner’s ability to run well: her aerobic capacity.

What is Aerobic Capacity? It is the runner’s ability to:

  1. Consume oxygen
  2. Transport oxygen
  3. Utilize 0xygen

The cardiovascular system provides the framework: Lungs, Heart, Blood Vessels, and Oxygen “transfer” to muscle cells (utilization). A basic explanation:

  1. The heart delivers a certain quantity or volume of blood via each stroke to the lungs to dispense waste and absorb oxygen into the blood. This is your ability to consume oxygen.
  2. This blood is redelivered to the heart for another surge into blood vessels that will carry the oxygen to the muscle cells. This is your ability to transport oxygen.
  3. As oxygen encounters the muscle cell membranes it is absorbed through the cell wall and is combined with a hydrocarbon chain (carbohydrate or fat). This causes a chemical reaction within the muscle cell and causes the muscle cell to contract. This is your ability to utilize oxygen.

Consuming Oxygen

At the bottom of your lungs are “capillary beds” – rich beds of blood vessels that absorb oxygen from the lungs. The density of the capillary beds determines what volume of oxygen can be absorbed per stroke of the heart.

When you train correctly, three things happen simultaneously with regards to consuming oxygen:

  1. Your heart gets bigger – the chambers enlarge allowing more volume of blood per stroke to reach the lungs.
  2. Your blood volume increases – more blood is now circulating and filling the enlarged heart chambers.
  3. More capillary beds “bloom” at the bottom of the lungs significantly increasing the “surface area” available for oxygen absorption.

It is thought that these capillary beds produce a “bloom” with every 6th week of training. As you might imagine, if you increase the surface area for the absorption of oxygen, a greater volume of blood is flowing with an increased density of oxygen. The heart has enlarged to accommodate the additional volume and no longer needs to beat as quickly to deliver the same amount of oxygen for same amount of activity. This physical change within produces an amazing outcome without – namely faster and faster paces at reduced effort.

Transporting Oxygen

Two words: Blood Vessels. Thank goodness we can grow more and more and more and… The trained runner has more of these pathways than not only the average person, but probably most other athletes. The reason? The entire sport is dependent on getting oxygen to the muscles for a sustained period of time. Therefore, if you open us up, you’ll find a virtual plethora of blood vessels all mysteriously leading from the heart to the legs. Hmmm… The legs are demanding this additional oxygen carried by additional blood pumped by a stronger, larger, more efficient heart.

The blood vessels become more elastic as they are subjected to greater stroke force carrying oxygen and other beneficial compounds (painkillers anyone?) produced by the body’s response to exercise. The net result is super blood vessels that are flexible, healthy and redundant. What would happen if you added a diet high in anti-oxidants like salmon, berries, wine, and supplemented with vitamin rich-fruit and vegetables? What then would be coursing through those blood vessels day in and day out???

Utilizing Oxygen

So you gathered up oxygen from the lungs, you pumped it down the tube, now what? Gotta use it…

When you eat, carbohydrates are broken down into simple hydrocarbon chains called glycogen. Glycogen is wonderfully stored in muscle fibers and your liver. Oxygen is required to combust this plentiful fuel. Carbohydrates that are not “burned” are turned into other hydrocarbon chains called lipids (fat). Both glycogen and lipids are appropriate fuel for running. Both need oxygen to “burn” thus the term “aerobic” which means “with oxygen”.

There are other combustion methods that do not use oxygen to break down a fuel molecule. These methods produce very short bursts of energy until the aerobic system can come into play. These methods are extremely inefficient, cause a significant build up of lactic acid in the blood, and for our purposes, entirely useless. Examples are the all-out sprint or the “flight or fight” instinct within us.

Again, the oxygen encounters the muscle cell membranes. As it is absorbed through the cell wall it is combined with a hydrocarbon chain (carbohydrate or fat). A chemical reaction occurs within the muscle cell and this causes the muscle cell to contract. The result of the chemical reaction is a recombination of the hydrocarbon chain into CO2 (carbon dioxide) and H2O and another product called Lactic Acid. Both the CO2 and H2O are delivered back through the membrane wall and into the blood for delivery to the lungs for exhalation. H2O also will be transferred through the pores of your skin as perspiration. The lactic acid remains in the blood and is reprocessed back into glycogen (blood sugar) via the liver.

Accumulation of lactic acid in the blood is what limits our ability to continue. If the accumulation becomes too great, the pH level of our blood drops to a critical level and the cramping you feel is the body shutting down aerobic combustion to preserve itself. How quickly and to what degree lactic acid accumulates in our blood is directly related to how fit we are. The less trained we are, the quicker we overwhelm the liver’s ability to “clear” the lactate from our blood. The details are complex but suffice it at this point to understand that the more we train, the less lactic acid accumulation and the longer we can run.

Next… Part 3 – How to train



4 Comments
  1. Melisa (Irish Blue) on June 5th at 7:30 am

    I really found this informative. Thanks!

  2. A Letter to Mrs. McCarthy*-Part One » Complete Running Network on June 6th at 6:11 am

    […] A Letter to Mrs. McCarthy*-Part Two […]

  3. Richard Edwards on June 21st at 7:50 am

    Iíve been reading for a while but this post made me want to say 2 thumbs up. Keep up the great work. Bill

  4. Carri Potts on May 22nd at 3:34 am

    I thought this was very informativie. I have worked up to running 3 miles a day but found this information very helpful in learing how the body works. Thanks a lot!

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