The Physiology Of Running
Know How A Runner’s Body Function And Optimize Your Workouts
The Essence Of Running
Basically, running is all about moving your body quickly from one place to another. Every movement needs energy. Efficient movement, in a runners context, simply means moving from one place to another with the least amount of energy at the fastest possible pace. This implies that we have a set amount of energy to use, during a run (which includes supplementary energy consumed as we run).
This amount of energy can be converted into movement at a given pace. To target our body with exercise, such that it works more efficiently, we need to know what is actually happening, and then design workouts to optimize these processes.
When we run, energy is produced in our muscles that contracts and sets our body in motion. This is a very complex procedure, where chemical energy is produced in the muscle cells and converted to kinetic energy, which moves our body. To get a fundamental insight into your workouts, we are going to look closer at the way these cellular processes take place. To do this, we will dive into the inner parts of our body.
The Runner’s Physiology
Each muscle in our body consists of bundles of muscle fibers. These are long threadshaped cells that are able to contract and make your body move. To produce a contraction of the fiber, we need energy, and this energy the muscles obtains from Adenosine-Tri-Phosphate (ATP). ATP is a molecule of a adenosine (A) and three phosphate (TP) bindings. In fact this is the muscles fuel, and it is the only fuel they run on.
Inside the single muscle cells ATP is broken down into Adenosine-Di-Phosphate (ADP), which releases chemical energy. This energy the muscles converts to kinetic energy. The decomposition, in chemical turms, looks like this:
ATP → ADP + P + Energy
If your muscles had unlimited ATP at its disposal, there would be unlimited energy to produce movement. Unless you are Superman this, unfortunately, is not the case, ATP is limited. Each cell only contains a very small amount of ATP that only last for a few seconds worth of work. This results in the need for you muscles to continuously having to recharge by creating new ATP. To do this they need another source of energy, and this energy is obtained by breaking down carbohydrate and fat, and to a lesser extent from breaking down protein. This is the reason Fat, Carbs and Protein are the three nutrients everyone is talking about.
Endurance And The Anaerobe And Aerobe Energy Systems
When your muscles recharges and creates ATP by breaking down carbohydrate and fat form your diet, it basically happens in two different ways: either with oxygen or without oxygen. This is why we talk of two energy systems of the body:
- Aerobe Energy System: Produces energy by breaking down carbohydrate and fat using oxygen in the process
- Anaerobe Energy System: Produces energy by breaking down carbohydrates and Creatine-Phosphate (CP) without using oxygen in the process
Creatine-Phosphate is stored in our muscle cells in the same way that ATP is. It differs from ATP as its purpose is to release large quantities of energy in a very short amount of time (approximately 4-10 seconds). This is why the body only breaks down the CP, when it is doing max workloads, and it is always done in conjunction with ATP. I any practical sense, CP is only relevant for short distance sprinters (100m, 200m and 400m).
The two energy systems, the aerobe and the anaerobe, are the only way the muscles can produce energy for movement. It has been well documented in scientifical research how these energy systems are activated at different distances:
| Distance | Anaerobic with ATP-CP | Anaerobic with carbohydrates | Anaerobic with carbohydrates and fat |
|---|---|---|---|
| 800 meters | 7% | 53% | 40% |
| 1,500 meters | 3% | 47& | 50% |
| 3,000 meters | >1% | 30% | 70% |
| 5,000 meters | >1% | 20% | 80% |
| 10,000 meters | >1% | 10% | 90% |
| Marathon | >1% | 2% | 98% |
Our First Conclusion: Your Aerobe Energy System Becomes Increasingly More Important The Farther You Run.
Breaking Down Carbohydrate And Fat
Although muscles produces energy by breaking down CP, we allow ourselves to omit it further considerations as it has next to no role in the production of energy during a 3K run or longer. The production of energy by the anaerobe energy system through break down of carbohydrates might be small, but not negligible, which is why it, together with the aerobe energy system, deserves a closer examination.
From 3K and longer distances your muscles pretty much gets all their energy from:
Anaerobe break down of carbohydrates: Your muscles can break down carbohydrates without needing oxygen, also known as glycolysis. This process is less important in long distance running, as the total amount of energy from this process is less than 20% for 5K up to the Marathon distance. Glycolysis primarily happens when the muscles are forced to work so hard that they cannot get sufficient energy through other processes. In chemical terms the process looks like this:
Glycogen → Lactic Acid + Energy (3 ATP)
or
Glycose → Lactic Acid + Energy (2 ATP)
The important enzyme ins the glycolysis is PFK (Phospho-fructo-kinase). The concentration of the enzyme in the muscles increases with exercise. As the concentration increases, the amount of energy to be got from the glycolysis.
Aerobe break down of carbohydrates: It is also possible for your muscle cells to break down carbohydrates with the use of oxygen. The first part of this process is exactly like the anaerobe process, but in the second phase a Krebs cycle occurs. This is the name for a complex series of chemical reactions that release energy, carbon dioxide and water. This energy is used to regenerate the ATP in the muscle cells, the carbon dioxide is expelled through the airways and the water is bound in our body. Aerobe break down of carbohydrates primarily takes place, when the muscles are working hard, but not hard enough to lack oxygen in the process. The chemical formula looks like this:
Glycogen + 6 O2 → 6 CO2 + 6 H2O + Energy (32 ATP)
or
Glycose + 6 O2 → 6 CO2 + 6 H2O + Energy (39 ATP)
Krebs cycle (citric acid cycle) uses CS, MDH, SDH which are enzymes that limits the process. The more of the enzymes you have the better flow you get in the Kreb cycle. The concentration of these enzymes can be affected through targeted workout.
Aerobe break down of fat: Lastly your muscle cells can break down fat to produce energy. This process needs oxygen to take place. The production of energy happens as fat decomposes into fatty acid that breaks down into energy, carbon dioxide and water. This is also a Krebs cycle, and produces a large quantity of energy. The chemical process looks like this:
Fatty Acid + 23 O2 → 16 CO2 + 16 H2O + Energy (110-140 ATP)
The production of energy needs large quantities of oxygen and thus only takes place at low intensity work. Vital for this process is the enzymes citrate synthase and HAD (3-OH-acyl-CoA dehydrogenase). This process has been analyzed in research studies and found to be an indication of the oxidative capacity of the muscle. Citrate synthase is important for the function of Krebs cycle and have been shown to have higher activity in runners with high performance than in ones with low performance. It has also been indicated that it is improved by training of varying intensities. HAD is an important enzyme for β-oxidation of fatty acids, it has been shown to have higher activity in high-performers than low-performers.
The Runner’s Physiology
Bacically, these are the three processes that decide how long and far you can run before you get tired. The two most important factors are whether your muscles produce energy from by an anaerobe or an aerobe process. This is important to know, as the anaerobe production of energy produces lactic acid as a biproduct, which accumulates in the muscles and lead to fatigue.
The next question of importance is if your muscles during aerobe energy production is using fat or carbohydrates as a source. The use of fat produces a lot more energy than using carbohydrates (110-140 ATP form breaking down fat opposed to 39 ATP from breaking down carbohydrates). The numbers here are not the important stuff, it is the ratio, that tells the story. Breaking down fat in the aerobe energy system, produces 3 times as much energy as using carbohydrates.
The Conclusion: The Better You Are At Breaking Down Fat In Your Aerobe Energy System, The Longer You Can Keep Up A Given Pace
The connection between optimizing your ability to burn fat and your ability to run long distance should be apparent. The muscles fat burning capacity is what we call endurance, this is your ability to last as your body does work. You can improve your endurance by focused training, mainly by running at low intensity and running longer distances. Your ability to last, your endurance, does have a natural peak, but it is a lot more plastic than you V̇O2max, and will yield much greater results over time, than working specifically on your maximal aerobic capacity (V̇O2max).
This is what prompts us to design training plans that primarily focuses on the development of your endurance i.e., optimizing your ability to break down fat into energy at as high a pace as possible. The better your endurance is, the greater pace you will be able to keep up at longer distances, this applies very much so from 10K and longer, but you will also see improvements in your 5K personal bests.
The hard part is to accept this insight, as you recognize that building endurance is a much longer game than increasing your V̇O2max. Doing intervals will no doubt produce results much quicker, but if you stick with the program, you will see even better results after your first round of fundament training. As a minimum, you will have to complete a 16-week training schedule (starter + foundation training plan), before you are certain to see results that outperforms interval training. But after this, you will keep increasing your endurance much more than you would ever be able to do, if you were focused on a no pain, no gain high intensity workout routine.
Every foundation training plan gives you a base, to focus on race day, through a specialized training plan. After completing your event(s), you can then again return to a foundations plan, and continue to build on the endurance already gained. This you can do for years without maxing out on your endurance potential, being the natural biological limit of your particular body.
Endurance And The Relation To V̇O2max
The point we are making at Greenmoor Running is not to solely focus on improving your endurance, but the point is that your endurance should be your overall first priority as a long-distance runner. The reason your endurance cannot stand on its own is that breaking down fat in your aerobe energy system, require a much larger quantity of oxygen than does breaking down carbohydrate in the same energy system. This means that your endurance depends heavily on your body’s ability to take in oxygen i.e., a high V̇O2max, also called maximal aerobic capacity.
At Greenmoor Running, we define endurance as a measure of your ability to break down fat in the aerobe energy system. Likewise, we define your fitness level as a measure of your maximal aerobic capacity (also known as V̇O2max). In short, your fitness level is your oxygen consumption in milliliters divided by your bodyweight in kilos. This describes your ability to absorb and consume oxygen, adjusted to your bodyweight. Physiologically your fitness level is conditioned by your cardiovascular system. It is a very complicated transport system, that brings the oxygen from your lungs via the blood to your muscle cells. How much oxygen your deliver to your cells is conditioned by your lung capacity and your heart’s ability to pump blood.
- Lung capacity: On average a young untrained person will typically be able to draw in 6 liters of air in your lungs per minute while at rest. During maximal work this increases to 130 liters of air. These quantities, you can improve by focused training. An average elite runner will have raised this capacity to about 200 liters of air per minute.
- Heart’s ability to pump blood: This ability is the main limiter of how much blood your body can absorb per minute. It is the read blood cells that transports the majority of oxygen from your lungs and out into your muscle cells. This means that the better a pump your heart is, the greater quantity of oxygen can be delivered to your muscles. This value is called your minute-volume, defined as heart rate multiplied by volume per heartbeat. Volume per heartbeat is exactly that, the volume of blood, your heart pumps out in one beat of the heart. When you do a workout, you primarily exercise and increase your volume per heartbeat. Your max heart rate is primarily dictated by your genetics and your age and does not change much due to exercise. The volume per heartbeat is, on the other hand, able to change significantly through exercise. At rest an average young person will pump 5 liters of blood per minute, while pumping 20 liters at max work. An elite runner will typically pump 30-35 liters of blood per minute, meaning that there is a lot to be gained, if we focus on increasing your volume per heartbeat.
The Respiratory Exchange Ratio
The ability to utilize the fat burning part of your aerobe energy system, is crucial in relation to how fast you can run (and maintain that pace) at long distances. This is an equivalent to fuel economy, when driving a car. The body has its own fuel economy, and we use the Respiratory Exchange Ratio (RER) as a measure for this.
A normal persons have a RER between 0,70 and 1,25. The RER is a measure of the ratio of carbon dioxide and oxygen when breathing out.
There is a correlation between the amount of energy obtained from fat burning and carbohydrate burning in the aerobe energy system and the RER. The total sum of energy is always 100%, distributed, when working in the aerobe zones, between percentage fat burning and percentage carbohydrate burning. When the RER is equal to 1, meaning that the exact same amount of oxygen and carbon dioxide is present in an expiration, the amount of energy obtained through fat burning is 0% and energy form carbohydrate burning is 100%. This relation is as shown in the table below:
| RER | Carbohydrates | Fat |
|---|---|---|
| 0.70 | 0% | 100% |
| 0.75 | 15% | 85% |
| 0.80 | 35% | 65% |
| 0.85 | 48% | 52% |
| 0.90 | 70% | 30% |
| 0.95 | 85% | 15% |
| 1.00 | 100% | 0% |
We define the aerobic threshold (AT) as a RER of 1,00-1,03. In regard to our training zones, this means that your AT will be slightly above the pace at which your aerobe energy system stops getting energy through fat burning. There are several ways for you to get precise RER readings at different paces.
- If you have access to a physician with wireless equipment, you can get a reading from a closed track. This measures the ratio of carbo dioxide and oxygen at different speeds, as you go round a track. This is how most professional athletes are tested. Be sure to get the values of your pace at the RER of 1, your Aerobic Threshold, and the pace at your VO2max. these are used to calculate your running zones.
- There is a lot of physicians who do tests on treadmills. This is a very reliable way of testing, although the margin of error is slightly above that of a track test. It can be done in half an hour, but be sure to specify what type of test you are looking for, and what results you need from the test. On the downside, it can be pricy. Be sure to get the values of your pace at the RER of 1, your Aerobic Threshold, and the pace at your VO2max. these are used to calculate your running zones.
- If you prefer saving the money, you can do a reasonably reliable self test. This is a good alternative to a professional test, and it is free and can be done whenever you have the time for it, and gives you a pretty good indication of you individual training zones, and you AT pace. Please visit our self test page, where you will also find the zones calculator.
Go to the Self test page.
Go to the Running zones calculator.