BREATHING DURING EXERCISE
So let's start very basic with the lungs and work our way up to breathing during exercise. The purpose that we have for breathing is to supply our body with oxygen and remove carbon dioxide from the body. Duh. Moving on.Our lungs work to inhale and exhale by being in a constant pressure gradient. This means that there is always a difference in pressure between the atmosphere and the pressure inside our lungs. You might have heard before that pressures (as well as concentrations) will flow from high pressure to low pressure. This works in the basic human principle of equilibrium (which is a stable equality). So since pressure flows from high pressure to low pressure that means that when we are inhaling there is a lower pressure in our lungs. Then as we exhale there is a greater pressure inside our lungs so the air flows out. Here is a graphic to help explain.
The respiratory system works as an integral part with the cardiovascular system/ the heart. These two systems are usually combined and called the cardiorespiratory system. The heart is responsible for transporting blood to and from the muscles of the body to supply the muscles with oxygen. When the blood is headed to the muscles it is full of oxygen. Then the muscles use that oxygen to create energy in the muscle cells and it allows your body to move. Then the blood returns to the heart with no oxygen in it and contains carbon dioxide. This then goes through the heart, is transported to and from the lungs (for the lungs to remove carbon dioxide and inhale oxygen) and then is circulated back to the muscles.
So this explains why our heart beats and why we need to breath. But what is the point of moving all of this oxygen and blood around? As my Exercise Physiology professor would say, "The point of this class is about one thing. ATP." ATP (adenosine triphosphate) is essentially our energy source. Our body has to make and use ATP for any energy that we expend. If we want to breath, it takes ATP, if we want to chew our food we need ATP. ATP is essentially that cash that our body needs to pay for the energy that we expend. So the link between energy and our cardiorespiratory is pretty simple in that our body needs ATP and our cardiorespiratory system is an important component in this ATP creation by moving and circulating oxygen and blood. Our body needs to make and transport this ATP throughout our body in order to give our muscles, organs, and brain the proper energy to keep working.How exactly do we make this ATP to get energy? Hold on tight because you are about to see a lot of big words. The first step to making energy is having energy to burn. The saying is you have to spend money to make money and this is true for our body as well. We need to have energy stored up in order to burn energy. This stored up energy comes from the food we eat! Our body can create energy from carbohydrate, fat, and protein stores. The most effective and productive form of creating energy comes from carbohydrates so I will focus on that cycle. Also, one very important component to creating energy is oxygen. Without oxygen (anaerobic) our body can create energy but only a limited number of ATP which equals less energy. So our body needs stored macronutrients and oxygen as the two main criteria to create energy.
All of these steps occur in the mitochondria which a organelle inside the muscle cell. The first step in creating ATP from stored carbohydrates is converting the longer carboydrate sugar to the simple glucose molecule (basic sugar molecule). Then once we have glucose, the next step is called glycolysis, which means the breakdown of a sugar. Our glucose is turned into a compound called pyruvate. This pyruvate is changed into a chemical called acetyl coenzyme A (ACoA). ACoA then enters the Krebs cycle which is a repeating cycle that creates 2 ATP and creates two very important chemicals called NADH and FADH2. Those H's stand for hydrogen (which I will get back to in answering our question about lactic acid). Then once we get the NADH and FADH, they go to the last step in creating ATP which is called the electron transport chain. To go to the electron transport chain there MUST be oxygen present. Once there, simply, the hydrogen that was attached the the NAD and FAD molecules are combined with oxygen (O2) and creates water. Then the chemical change causes ATP to be produced and exported from the inside of the mitochondria into the cytoplasm. Once this ATP is produced it will quickly be grabbed again to start this entire cycle over again by using ATP to breakdown glucose. So again, you have to spend a couple ATP in order to start this entire process but there is a large positive profit from each cycle. Once again this is a VERY VERY brief breakdown of how the cycle works but it displays the basics which are:
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| Easiest and most simple image of this process that I could find. |
- We start with glucose and it gets transformed into a chemical called acetyl CoA
- Through the Kreb's cycle we get a large portion of the FADH2 and NADH (we get this from other parts of the cycle as well, just largest portion from the Kreb's cycle).
- Then, only if oxygen is in the cells (aerobic) the NADH's and FAD's go through the Electron Transport Chain to create ATP.
- If oxygen is present we create 36 ATP for each molecule of glucose and if no oxygen is present we only create 2 ATP for each molecule of glucose.
Through this whole cycle we are accumulating excess Carbon Dioxide and Hydrogen that need to be either used or expelled out of the cells. The hydrogen has to be combined with oxygen to create water. So essentially, when we create ATP (energy) we end up with 6 extra CO2 molecules and hydrogen that needs to be combined with oxygen to create water. This is where the cardiorespiratory system comes into play. The lungs are inhaling O2 and that oxygen then combines with the hydrogens in the mitochondria via the bloodstream. Then once the blood hits those working muscles our body sends back the carbon dioxide and water back to the heart and lungs to be expelled and repeat this cycle over and over.
SO, to finally answer the proposed question of why we breathe heavy during exercise, the easy answer is: to supply our body with the needed oxygen to keep up to the energy demands our body is requiring during exercise. There is a longer and more complicated answer but essentially, our bodies are requiring oxygen to complete this ATP process and if we are not able to supply enough oxygen we will not be able to produce enough energy (ATP) and we will get a buildup of CO2 and hydrogen in the body. I want to try and express how amazing our body is when it comes to creating ATP. During a run of 50km (31 miles) with a completion time of 2 hours and 45 minutes (which is moving smoking fast) our body will produce around 78.4kg of ATP. That means our body will produce around 172 POUNDS of a tiny molecule during one run!!! That blows my mind. That is how fast that cycle is constantly working and pumping out ATP for our body during exercise.
LACTIC ACID ACCUMULATION
My last comment above about a buildup of CO2 and hydrogen answers the other question I proposed earlier. When we are not breathing enough (or working harder than we are used to) we will get a buildup of CO2 and hydrogen ions in the muscle cells. This happens because we are not consuming enough oxygen/ producing CO2 faster than we can get rid of it. The real truth is that the hydrogen ions are the main reason that our muscle get sore and burn! Lactic acid has taken the bad rap for this, but the real cause is HYDROGEN. Lactic acid is a product of fermentation, which is when the skeletal muscle converts glucose to lactate during short and intense exercise (anaerobic exercise- no oxygen). SO we do create lactic acid when we go through brief and intense exercise which is when the muscles burn. But the difference between lactic acid and hydrogen ions is that lactic acid can actually be transformed back to pyruvate. Pyruvate (look above) is actually one of the steps in the aerobic cycle above. This means that although Lactic acid is not ideal, it can still be used to create and stimulate the ATP aerobic cycle!
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| Lactate can be turned back to glucose! |
Lactic acid has the bad reputation for causing muscle soreness but in reality, lactic acid can actually be used and created back into a necessary molecule for creating ATP, while hydrogen ions cannot be reused and need to combined with oxygen to continue to be useful. You don't need to understand what any of those terms mean in the picture above but you can see that there is an arrow that goes back to glucose! An excess buildup of hydrogen ions therefore are the waste product of exercise that cannot be useful for energy and therefore buildup in the muscles and cause soreness.
THE VERDICT
To sum up everything I talked about today: Our bodies main purpose is to create ATP to allow our muscles, organs, and brain to function properly. This is done by combining glucose (or fat or proteins) with oxygen to complete the aerobic metabolism which is the most productive way to create ATP. Our body needs the lungs and our heart/blood stream to transport oxygen and carbon dioxide to and from our cells. By keeping our oxygen levels high enough we will stay at a nice equilibrium where we are creating enough energy for the exercise or workout we are doing! At this equilibrium we will not be creating more CO2 and hydrogens than we can use up. We get into trouble when we are working too hard and we get this buildup of molecules (see last week's comment on VO2 max). The more in shape we are the better our heart and lungs become at transferring this oxygen to and from our muscle cells. This means that we don't have to breathe as hard or fast to get all of the oxygen to our muscles. This is why in-shape people won't be out of breathe on a 1 mile run while someone that is out of shape will be gasping for breath. I hope this all made sense!
NEXT WEEK: HOW TO EAT HEALTHY ON THE GO!
