The Energy of Distance Running: How your body keeps itself moving during a race

Throughout my running career in high school, I have had a fairly limited knowledge of the biology behind running. Most of my knowledge comes from two books I have read Born to Run, and Marty Liquori's Guide for the Elite Runner. Born to Run focused more about human's natural ability for endurance running and the running man hypothesis, which suggests that humans literally ran animals to death to hunt before the development of hunting weapons. However, Liquori's book provided me with some valuable advice as a distance runner: the difference between anaerobic and aerobic running. This information suggests that going too fast in the beginning of a long distance race will put too much stress on one's anaerobic system, which can negatively affect performance. Also, it provides reasons for training both aerobic and aerobic systems, and the difference between training each.

I have definitely used this information to my advantage. I would consider myself and the rest of the boys on the cross country team to be smarter racers and trainers than our competition, as we write plans to improve performance and always make sure to run a smart race by not going out too fast in the beginning of races.

Running, like most all of our movements and actions, is powered by ATP. Adenosine triphosphate (ATP) is broken down to provide energy for reactions in the body. A reaction in the mitochondria of muscle cells removes one of the phosphate molecules, releasing a large amount of energy to power things such a muscle contraction and movement (running). This leaves Adenosine diphosphate (ADP). This seems like this works perfectly right? Your body just continues to supply your muscles with energy through, ATP granting you unlimited energy. Except there's just one problem. Your body doesn’t have an unlimited supply of ATP. In fact, the human body actually has very little ATP stored  “on deck.” The body usually only has enough ATP gathered to power about four seconds of energy. So how does one's body supply itself with a consistent amount of energy during strenuous exercise like a race from anywhere in between 100 meters and a marathon?

There are three pathways where the body produces ATP when running: the phosphagen system, the anaerobic system, and the aerobic system. These each work at different stages to provide the body with ATP when running.

Figure 1-The Three Systems Used For Running

As soon as your initial supply of ATP runs out, you begin to utilize the phosphagen system. This system, also called the ATP-Creatine Phosphate System (CP), provides energy for in between 5 and 10 seconds after ATP storage is exhausted. In this system, creatine phosphate helps quickly resynthesize ADP into ATP by donate a phosphate group. This produces only one molecule of ATP for every molecule of CP, so CP storage depletes quickly. This system is used within a short race such as the 100m. Top sprinters have been found to have a large supply of CP.

Next, your body utilizes lactic acid fermentation to provide energy through anaerobic glycolysis. This is used primarily in the next 30 seconds to 3 minutes to provide the body with energy. Glucose is broken down to form two molecules of pyruvate, which is then used to create ATP. This pathway creates 2 molecules of ATP However, this reaction also creates a waste product called lactic acid which can cause muscle soreness and fatigue during and after running. The increased muscle contraction caused by lactic acid makes it so this pathway can only be used for a maximum of around 3 minutes. This would be ideal for a race like an 800, which would last anywhere in between around 1:50 and 3:10 for high school runners. Distance runners train to increase the efficiency of their anaerobic system by doing track workouts or "speed work" which usually involves doing repeats of a short distance. Also, when a runner calls upon a final last burst of speed at the end of a long race, they are using the anaerobic system.

Finally, when all other systems have been used, the body turns to aerobic respiration, which will be the primary provided of energy until one has stopped running (hopefully from finishing the race and not from passing out!). This utilizes the Krebs cycle, the electron transport chain, and aerobic glycolysis to generate a huge amount of 38 ATP for every molecules of oxygen, making this the most efficient system. This is heavily used from basically any race from an 800 meter run (half a mile) to a ultra-marathon, and is also relied heavily upon in training. It uses carbs, fats and proteins in reserves to generate this energy. Distance runners do heavy aerobic training such as long runs to increase their aerobic capacity, or how efficient their aerobic system is. Good endurance runners have a much better base aerobic capacity than the average human, but anyone can increase their's with training.

Figure 2- Amount of ATP Each System provides your body over time

If I had to sum things up to illustrate roughly where you get your ATP from during a race, it would look a little like this:

Overall-
1 to 4 Seconds-ATP energy reserves
5 to around 15 Seconds- Phosphagen System Provides ATP
16 Seconds to Inbetween 45 seconds and 3 minutes- Anaerobic System
45 Seconds/3 Minutes to whenever- Aerobic System

100m Run
1 to 2 Seconds-ATP energy reserves
3 Seconds to Finish- Phosphagen System

800m Run
1 to 4 Seconds- ATP Reserves
5 to 10 Seconds- Phosphagen System
15 Seconds to 45 Seconds- Anaerobic System
46 Seconds to the end- Aerobic System