Why is Oxygen so important?

Running involves a lot of different aspects of how your body operates.  A lot of research has been dedicated to the biochemestry and physiology of what is involved.  I have become so fascinated personally that I studied a lot of this to better improve myself as a runner.  I think it is very beneficial to anyone who takes running seriously that they study the science behind how their body functions.  There is so many things to explore so it may be very confusing.  From energy Gu's to training plans to VO2max speed workouts to 20 mile long runs to minimalistic/stability shoes...  there is so much to learn.  So let's start by getting down to the very basics.  In this blog we will learn about running's most precious and vital resource: Oxygen.  Because when you get right down to it, oxygen is really the most precious resource for a long distance runner.

In the most very basic way to describe running, all it really is: a bunch of muscles working together by a series of muscle contractions repeated over and over again.  A muscle contraction is the activiation of tension or force generating sites within muscle fibers.  Err... ok, in laymens english let's look at one type of muscle contraction, concentric action in skeletal muscle. When we say skeletal muscle we are talking about the type of muscles that connect our bones together so they can move our body on command (as opposed to cardiac muscle which allows our heart to keep pumping without us thinking about it; and smooth muscle which allows our other major internal organs to do their job also without thinking about it).  All skeletal muscle connects to bones via the tendon. 

So picture our arm straight out in front of us (palm facing the air).  Now move your fist towards your shoulder to bend your arm at the elbow.  To make this movement, your brain first made a command to your bicep muscle to concentrically contract (or shorten).  This message went from your brain through the nervous system down to your bicep muscle.  The fibers in your bicep muscle concentrically contracted so that they pull on the tendon that connects it to your forearm bone which in turn made the arm bend at the elbow.  Now suppose in the same arm you were holding a dumbell weight.  Now if you relaxed your arm, gravity would just swing your arm down towards the ground so the weight would bang against your thigh or hip area.  Now think instead that you carefully moved your arm in a controlled manner so the weight would not drop so forcibly.  To do that, your bicep muscle lengthened in the opposite direction by performing what is known as an eccentric contraction.  Now let's say your elbow was bent at a 90 degree angle and you held that weight in a steady position.  Your bicep muscle is not moving, but it is still exerting force against gravity through isometric contraction so that your arm does not fall further towards your thigh/hip.  You can feel the force after a few seconds as you hold your arm in place because your bicep muscle will fatigue very quickly.  In fact, hold it long enough and you will feel it burn. 

Running is all about all 3 types of muscle contractions being performed by your arms, legs, shoulders, chest, back, stomach, glutes, and hips.  A series of muscle contractions being performed over and over and over again.  Eventually your muscles will fatigue which will impact your performance.  But how does it fatigue and what can I do to prevent or delay this fatigue?  This has been a study since 1890 by a physiologist by the name of Angelo Mosso in Turin Italy.  He was studying the effects of frogs legs that were artificially being contracted by exciting the muscle with voltage from electrodes.  When the frog legs were no longer reacting to the voltage, he studied the biochemestry and found what he called the "toxin": lactic acid.  Lactic acid was supposedly forming in the muscle of the dead frog which he concluded was the cause of the muscle fatigue.  (Later on, science discovered that is what lactate not lactic acid that was forming.)  Mosso was following up on Ludimar Hermann's discovery in 1871 that muscle tissue can continue work without a sustained oxygen supply.  It was later found that blood lactate was caused when the muscle fiber was excited when oxygen was not present and that this lactate disappeared with an abundance of oxygen.  Otto Meyerhof in the early 1900's discovered that blood lactate could be converted back into glucose sugar in the presence of oxygen and later on came up with the basis theory behind Glycolysis (where glucose sugar was used to perform muscle contractions without oxygen which resulted in lactate).  He built upon the discoveries of Buchner, Harden, and Young in similar discoveries on the fermentation of yeast. This lead to further research on the effects of "oxygen debt".  This eventually lead to Karl Lohmann's discovery of adenosine triphoshate (ATP) in 1928.  In 1934, Lohmann and Meyerhof associated ATP as the energy supplier for muscle contractions.  They also discovered that creatine phsosphate was used to transferring a phosphate group back onto ADP to reform ATP. 

In a nutshell, running is all about biochemestry.  Turning glucose sugar into ATP which is the real fuel behind all your muscle contractions.  Fatigue in muscle is caused when the work of reforming ATP is happening when glucose sugar is used without enough sustained oxygen supply. 
Let's start with a couple of videos on how ATP is used to influence the contraction of muscle fibers through a series of biochemical reactions called the Cross Bridge Cycle (or sliding filament model).

And this video on how celluar respiration through Glycolysis, Krebs Cycle, and ETC is used to re-create ATP.

So now we know how muscle contractions are fueled, and how glucose sugar and oxygen molecules are used to produce the currency for causing movement.  Let's look at what happens when we try and do this without enough oxygen. 

So when we run (or perform any type of exercise), we create a demand for energy. That demand for energy requires our body to transfer the stored energy we have (to keep it simple let's just focus on glucose sugar) into ATP.  The longer we perform the exercise, the longer we create this demand for transferring glucose into ATP.  The amount of demand is dictated by the intensity of the exercise.  The more intense the exercise, the bigger demand for energy we cause.

We have already learned that oxygen has an important role in transferring this glucose sugar energy into ATP energy.  But we also learned that glucose sugar can be transferred into ATP without oxygen by the process called glycolysis.  But in order to keep glycolysis running without oxygen, the pyruvate which is resulted from glycolysis is fermented into lactate.  This is very similar to how sugar in fruit is fermented by say yeast without the presence of oxygen to produce alcohol.  We learned that we intially attributed lactatic acid to the cause of fatigue, causing a burn that was dubbed lactic acidosis. (Remeber above when we were holding that dumbell in our hand and kept our elbow bent at 90 degrees for a period of time?)  It wasn't until 2004 when Robergs, Ghiasavand, and Parker discovered that the real culprit of fatigue is not from the lactic acid during glycolysis, but from a build up of hydrogen protons that are caused when ATP is broken down into ADP during the cross bridge cycle.  Normally this build-up of hydrogen protons is consumed during the aerobic processes of the Krebs Cycle and ETC and during creatine-phosphate ATP regeneration.  But when the anaerobic process of glycolysis overtakes the aerobic process, the build-up continues which causes the pH in the muscle to drop which causes acidosis.  It just so happens to be coincidental that hydrogen protons exist during glycolysis that caused early psysiologists and biochemists to make the erronous connection to muscle fatigue. 

Because science has not caught up to exercise enthusiasts and coaching, the notion of lactic acid caused by anerobic exercise still causes some confusion today.  However, it is still valid to note that it is an exercise intensity that causes a demand greater than what our sustained oxygen supply can be used to maintain aerobic activity that causes a build-up up hydrogen protons which acidizes our muscles which causes fatigue.  The intensity that causes glycolysis to overtake the aerobic system to meet this increased demand causes a phenomon called oxygen debt.  When exercise intensity is just enough to cause a demand that is equal to our capability of using oxygen to burn glucose to form ATP, we call this steady state.  During steady state, the build-up of hydrogen protons is insignificant because our other metabolic processes will consume the excess hyrogen protons.  It's only when exercise intensity becomes so great that an oxygen debt forms and we no longer can consume the excess hydrogen protons and instead they accumulate in the muscle cell. 

Even when we are done performing the exercise, we still have a build-up of hydrogen protons and lactate that must be converted back into glucose.  Since exercise is done, oxygen levels can slowly go back into a steady state.  But before steady state can occur, some of that post oxygen consumption must be used to transfer that lactate and hydrogen protons back into glucose.  This is known as EPOC (excess post-exercise oxygen consumption).  It's why you continue to breath hard and expell lots of carbon-dioxide for a few more minutes even when you are done with the workout.  This EPOC is sometimes known as the after-burn.  You continue to burn calories at an accelerated rate during this EPOC stage.

So if you didn't quite understand everything so far, understand this.  Your muscles need energy to move so you can run.  Oxygen is used to burn stored sugar inside the body to make this energy.  If you run at a pace that is very confortable, you have a demand that can be met by the amount of oxygen that you can breath in.  This is known as steady state (the intensity matches your oxygen supply).  If you start to run at a faster pace to the point where is starts to become uncomfortable, the anaerobic process has to work overtime to meet the increased demand of energy.  When this happens, we have what is called an oxygen debt.  When oxygen debt occurs, a slow build-up of hydrogen protons occur in the muscle tissue which causes acidosis which causes severe discomfort to the point where the muscle is no longer able to contract. 

So why is oxygen the most important resource to a long distance runner?  Because the body is much more complex.  The body is able to use fat stored in the body as well as glucose sugar to fuel muscle contractions for a very long time.  Just as long as the intensity of the exercise doesn't cause oxygen debt.  But once we increase the intensity to the point that demand for energy out paces the oxygen we can supply to meet that energy demand, acidosis will occur.  It is this acidosis that will cause muscle fatigue way before we run out of glucose sugar that will make us quit.  The better we can train our body to deliver more oxygen to our muscle cells, and the better we can train our muscle cells to use oxygen, the more demand for energy we can sustain without this acidosis to occur. 

As a new runner, train to use oxygen better.  Don't train in a way to use more sugar.  I see this all the time when new runners ask about Gu, and other fuel to consume while running.  There is even lots of talk about what to eat before you run so that you can have more energy to run.  While this is all good for maximum performance in a race, it is truly unnecessary to worry about during brief training sessions that last less than 90 minutes.  Just as long as your intensity level remains at a comfortable steady state level.  Or as we already discussed, at an easy conversational level.  We should have learned in my last blog that lots and lots of conversational easy runs will improve the strength of the heart, and all the body's functions to deliver and use oxygen more efficiently.