Energy systems and running

This post is a follow on from my post prompted by an England Athletics Endurance day.

I am interested in this area, but am not a sport scientist.  I favour sports scientists who will say, I think this is right, but there is still work to do to prove it.  Healthy scepticism is good when reading sports science literature.  If you think I am wrong, then please comment on what I am saying.

The traditional model for energy systems within running is that there are three main energy systems.  These are ATP/CP (adenosine triphosphate and phosphocreatine); oxygen-independent glycolysis (normally referred to as anaerobic) and aerobic.  This is a significant simplification.

The normally accepted view is that the energy systems are used almost one after the other.  The ATP/CP system turns on when the first vigorous movement occurs.  There is ATP stored in the muscles, enough to last around 2-4 seconds.  This creates ADP when used.  The CP stored in the muscle combines with the ADP to create more ATP.  There is enough CP stored to produce another 5-10s of energy.  When these stores are depleted, the glycogen stored in the muscle is converted without the use of oxygen to create more ATP (creating lactate in the process).  This can last for around 1 to 2 minutes.  When this is used up, liver glycogen is transported to muscles to be used with oxygen or aerobically.  This process is much slower than the previous two, limiting the amount of energy that can be provided, so you have to slow down.  After the liver glycogen is used, the body is forced to use fat and then, much later, protein.

These energy systems exist, and scientists are getting better at understanding them.  However, it is hard to believe that this overall scheme is actually how energy systems really work.  The best book I have read so far on this subject is “The Lore of Running, 4th Edition” by Tim Noakes. The first few chapters of his book effectively rebut what he calls the Cardiovascular/Anaerobic Model.

I have have tried to think of how this energy model would work in a fell race or orienteering event.  As you set off, the muscles use up the ATP/CP supplies quickly.  Then, for the next couple of minutes, the anaerobic system provides energy before running out.  Finally, the aerobic system comes in and the body has to match pace with the available, reduced, energy supply.  It is widely understood that the anaerobic system cannot replenish during exercise.  So, how is it that I can summon the energy to jump across a river, run hard for a style to get in front of a competitor, or even pick up the pace to sprint at the finish?  All of these would appear to require levels of energy that the aerobic system cannot supply, so the model simply doesn’t work for me.

A subsequent post will talk about Noakes’ “Central Governor” model, one which begins to make a lot more sense to me.

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