Dear Runners,

This week I have prepared a review of what is going on in our bodies at this point of the training.  I prepared this quasi-complex answer to respond to a quasi-simple question.  That question is “why should we run slow on the long runs even if it feels good to run fast?” 

At this point in the training it’s difficult to run slow because after a few weeks of training, our respiratory and cardiovascular systems are starting to adapt and it is becoming easier to go faster.  And after all, don’t we need to run fast to get faster? 

The answer is yes, we do need to run faster to build our speed.  But there is a time for fast run training and a time for slow run training.  We run slow(er) to allow our bodies to adapt and grow aerobically.  This is important because improving our aerobic energy system (and other systems too) improves the ability and efficiency of the main energy producing system we need for distance running.  If we just run fast all the time, this adaption will not be as efficient. 

So even though it does feel good to get out there and stretch the legs with a good hard run, we should respect the purpose of each phase of training we’re in. Even though we are starting to work on speed building we also need to continue to build our base as well. 

If you run in my group you have probably heard me talk about how the purpose of our current running is to build a bigger running engine.  Think about this as a metaphor.  Right now we are all running with engines that have 4-cylinders.  They get the job done but they have to work pretty hard.  What we want to do is build engines that are like big supercharged V8s.  So when we put that engine in gear to run 13.1 miles it has all the power it needs to pull us along without revving out of control or becoming fatigued.  The basebuilding phase does its work by making our running engine bigger. 

When we train our bodies aerobically several major adaptations take place including: muscle adaptations (increased muscle size through bigger fibers), capillary density (increase in the body’s ability to move oxygen to the muscles), myoglobin increase (increased ability to transfer oxygen to the mitochondria), mitochondria density increase (provide more energy producing ability) and finally aerobic enzyme increase (improve body’s ability to convert fuel sources to produce ATP).

Here is an extremely condensed version of the science.  Our bodies produce a substance called ATP (adenosine triphosphate) which acts as the fuel for the muscles.  Depending on how quickly and how efficiently your body produces ATP determines how long before your muscles reach fatigue.  And there are three systems your body uses to produce ATP – the creatine phosphate system, the aerobic (with oxygen) system, and the anaerobic (without oxygen) system. 

The fuel for the aerobic system to make ATP is glucose (carbohydrates) and fats.  Of course, there also has to be oxygen.  Aerobic energy production takes place inside structures in the cell called mitochondria. This system is the one most in play for distance runners. 

Anaerobic energy production uses glucose to produce ATP.  This glucose can come from carbohydrates and can also come from glycogen in your liver or muscles.  This system is used primarily for intense levels of training where large amounts of energy are needed or when energy is needed very quickly. 

The creatine phosphate system is the simplest and fastest way to produce ATP.  Unfortunately, there is a very limited supply of phosphocreatine and it is used up in about 5 to 20 seconds.  So it doesn’t help much for distance runners. 

Running fast requires that your body produce ATP fast.  Production of ATP is primarily the result of metabolism of either glycogen or fat.  Protein plays only a minor role. Glycogen metabolism takes fewer steps, so it is a primary source of ATP and can produce it pretty fast. That’s the up-side.  The down-side is that in addition to the ATP, the by-product of this metabolism is pyruvate – which can either become Lactate OR go on to produce more ATP if (a big IF) there is enough oxygen available and there are enough mitochondria available to further metabolize the pyruvate.  In other words pyruvate is both a byproduct as well as a potential source of energy.

The problem is that if pyruvate is being produced faster than it can be used it changes into lactate – which then needs to be shuttled to other mitochondria OR to the liver where it can eventually be changed back into glycogen.

The bad news with this shuttle stuff is that high levels of blood lactate are associated with a limited time to exhaustion – so it’s in your best interest to produce pyruvate at a rate it can be subsequently utilized to make more ATP.  

You can limit the production of pyruvate by using fat for fuel.  This is done when running aerobically. Fat is metabolized in the mitochondria and does not produce pyruvate/lactate as a byproduct.  You can also affect blood lactate levels by making your body better able to utilize lactate for fuel… that means making more mitochondria and making the ones you already have bigger.   Again, another body adaptation brought about by aerobic training. 

So running at easy aerobic paces builds the aerobic and muscular infrastructure to support the faster pace running when the time comes.  And building your foundation first will set the stage for success in the faster running later. 

During those runs we can work on faster pace training to work on the specific neuromotor programming and physiological infrastructure needed to run faster and to get your body used to the pace and used to producing ATP and transporting oxygen at a rate that will sustain that pace.  

See, pretty simple. 

Obviously, it isn’t important that you memorize this information.  But what you should take away is that running slower will train our aerobic system.

Running faster will push our bodies to the anaerobic training point and the effects on the body are different and ultimately will hold our training back if done too often. 

Let me know if you have any questions and I look forward to seeing you Saturday when we will go for a nice sloooooow run. 

Run well…

YouTube Video

Okay, this video cracks me up every time I watch it.  The complete difference in physical ability between the two runners always makes me laugh.   Enjoy!

Run well…


Shawn Herbig is an RRCA Certified Running Coach.  In his day job he owns a market research and data analytics firm called IQS Research. 

© 2013 Shawn Herbig.