If your body thinks something is important to its survival, it will build that up beyond what it needs to survive. You’ve probably figured out that if you hold your breath for more than a few minutes, death soon follows… or at least an insane desire to breath. That is how important the lungs are. Without oxygen the body will die within minutes, and so it is one of the most robust, redundant and carefully controlled systems in the body… and we swimmers tend to mess with it a lot, so let’s see how it all works. (oh… and there is more to it than just O2).
First off we need to understand how to get outside air inside the lungs. The body uses muscles just like any other. At rest, you use the diaphragm and external rib muscles (called intercostals = “between ribs”). When they contract, they expand the chest, which creates a negative pressure, and air is sucked in by the mouth, nose, and windpipe (called the trachea, the hard thing in front of your neck). Expiration at rest requires no muscles at all. The inspiration muscles relax, the chest wall recoils and pushes air out.
But, when you exercise things get a little more force-full. Four extra muscles jump in and help with inspiration, and expiration becomes forced, using internal rib muscles and the abdominals (ever wonder why you have trouble breathing when you’re doing ab workouts in dryland)? So why are we talking about all this? At rest, these breathing muscles use up about 2% of the O2 you breathe in. But at maximum exercise, that number can jump to 15%. That’s a big chunk of energy that is not going to your muscles to help you swim faster. Luckily, these muscles like any others can be trained and improved.
Tangent: athletes using breathing assist device had improved performance because they didn’t have to spend as much energy breathing and could focus the extra energy on their muscles… implantable battery powered breather?
As the air is being sucked in, it passes through a series of tubes called bronchioles (from the Greek for “windpipe”) which have smooth muscle surrounding them (just like arteries and veins). These smooth muscles can contract, closing the bronchioles and control where air goes in the lung. I only mention it here because these bronchioles are a big problem in asthma, exercise induced bronchoconstriction, and COPD in smokers (more in the Injury lesson).
At the end of these tiny little windpipes is the alveolus (which his Latin for “small cavity”). An alveolus is a microscopic balloon filled with air. This is where the magic happens. You see, all your body has to do to get enough O2 is to expose every cell in the body to air. Since there is less O2 in the cell (because it is being used up by mitochondria), O2 from the air will naturally diffuse into the cell. Obviously this is not possible, most of the cells that make up our body are deep underneath layers of tissue, and exposing them all directly to air would require that you take the shape of a pancake one or two cells thick. Instead, the alveoli do this for you. They increase the surface area of the lungs to 50 square meters, or the size of half a tennis court (compared to your skin surface area which is 1.5 square meters)!
Tangent: Emphysema is a disease where you lose alveoli. The decreased surface area means these patients can’t get enough exposure to O2 in the air. They have trouble breathing even at rest, and eventually suffocate to death. Main cause… smoking.
Just having a lot of surface area exposed to air is not enough, which is why blood vessels and capillaries surround each alveoli and expose moving blood and red blood cells to the air being held in the alveolus. As the de-oxygenated blood coming from the right heart goes through the capillaries in the lung that surround alveoli, the hemoglobin inside the red blood cells “pickup” O2 (and dump out CO2) as they continue back to the left heart to be pumped out to the body.
At rest, the red blood cell spends about one second passing through the lung capillary from beginning to end; but it only takes 0.25 seconds to fully exchange CO2 for O2. Because of all the extra time given to red blood cells to do their job, blood flow can be quadrupled (say when exercising) and still see no drop in O2 saturation. That means ALL of the passing red blood cells get fully saturated with O2, even at maximal exercise. So we thought… some very very very elite endurance athletes will have such high and fast blood flow through their lung capillaries that the blood doesn’t have enough time to pick up all the O2 it could, so these athletes see a drop in O2 saturation during intense exercise. It does not seem to have a bad effect on their performance.
Tangent: So if all your blood fully picks up O2 as it passes through the lungs, then why do athletes suck on O2 on the sidelines? How is supplying more O2 going to help if you are already saturated? The mind is a powerful thing don’t you think…
That is all of lung anatomy, pretty simple. Suck in the air, spread it out over a large surface area, put it next to passing blood, and then send it back out and repeat. Gills work the same way, except instead of air, fish pass water next to their capillaries and pick up O2 that is in the water.
As we said in the Cardio lesson, cardiac output can increase…a lot. And all that blood has to go to the lungs during every trip around the body. Blood flow from the left and right heart must be equal all the time, otherwise all your blood would pool up in the lungs or in the body (this happens in heart failure). That means blood flow to the lungs at rest is really small compared to when you are exercising. During those times you aren’t sending a huge amount of blood to the lungs, and a lot of the capillaries (mostly in the upper lungs) are closed for business. During warmup however, cardiac output goes up, blood flow increases and those shut capillaries open up and allow more blood to be oxygenated by the lungs. Some say this is the cause of “second wind.”
Remember how we said in the Cardio lecture that training your muscles will cause the capillaries around them to grow and extend so that they can better supply the muscles? The same thing happens in the lungs. Over time, and with training, the capillaries in the lungs will grow so that more and more blood can be oxygenated at the same time. The number of alveoli however stays the same.
Before moving on to the “why you feel like breathing” section, one more point about lungs that a lot of swimmers and coaches forget. The lungs are basically big bags full of hot air. Air floats, and so when swimming, there is a “floating force” (buoyancy) that pushes your chest up in the water. In order to maintain good sea-saw alignment in the water, coach says things like “swim downhill!” Your lungs are why that is tough to do, they don’t want to sink, but all good swimmers must learn to press down with their chest and feel like “swimming downhill” in order to force good body position in the water. Pressing the chest down in the water requires pretty strong abs (like doing a plank while you swim), and when you’re tired… say at the end of a 200 race, your abs give out and your chest rises causing you to go vertical…very bad.
It’s a little complicated…
Like we said before, if something is going to kill you fast (like low blood sugar or running out of O2), the body develops redundancies to prevent those things from happening. That is why multiple paths exist to create the sensation of “TAKE A BREATH.” Three of the biggest reasons for that feeling are O2, CO2 and pH (acidity). Your body wants to keep all three of these within their limits, and the best way it can do that is by controlling breathing.
Tangent: The complexity of breathing has limited our understanding. Some parts of the body that control breathing and measure CO2 and O2 in the blood rarely see changes in those compounds, so how are they controlling breathing!?
CO2 has to be held in a narrow range in the blood. If it goes up you will feel like needing to breathe, and if you hyperventilate your CO2 will drop and you won’t feel like you need to breathe. CO2 levels can change very fast and it has a fast effect on breathing too.
O2 on the other hand does not go down very fast (because it does not dissolve in water as well as CO2), but when it does it creates a very big change in breathing, much stronger than CO2. That makes sense… the second your body feels like it is running out of O2 it will want you to get it back. In fact, O2 trumps CO2 and we see this in two places. During exercise, breathing to maintain O2 will sometimes be high enough where too much CO2 is lost in the lungs, and your blood CO2 will drop below the “normal” range. And at altitude, your body is struggling to fill all the red blood cells with O2, so the increased breathing will also decrease CO2 in your body.
Keeping O2 in the blood is the body’s highest priority, but keeping the blood pH in a narrow range is also important. Any deviation from the normal 7.35 to 7.45 pH will cause a breathing change to “buffer” the pH by getting rid of CO2 during low pH (acidic blood) or keeping CO2 during high pH (basic blood). We will see in a little bit how CO2 and acid are basically interchangeable and the body can control one through the other. What would happen if your pH changed too much? Proteins work by taking specific shapes to do their job. The proper shape depends on pH. Once that shape is lost, it won’t come back, and you’ll die... bad.
So how does all this work together in real life? You probably notice that as soon as you start working out, your breathing goes up fast to keep up with the demand. This is controlled by neurons which sense changed in O2, CO2 and pH, automatically increasing breathing to keep the body happy. What you don’t notice is that the longer workout goes, the more and more you breathe even if you are doing the same intensity of work (say a real long set of 20x200s). This slow increase in breathing is due to hormone changes and it is really unclear why that happens. (We will talk more about hormones in a dedicated lesson).
When you stop working out, the same thing happens in reverse. There is a quick decrease in breathing due to nerves, and a slower and gradual decrease due to hormones. The way your body controls this increase and decrease means more to swimmers than other sports. At first, your breathing increases due to a combination of deeper breaths and more breaths per minute (these are called tidal volume and respiration rate). But at high exercise intensities, only respiration rate increases because the depth of breathing is maxed out. A runner doesn’t care about this because they can take a breath whenever they want. But swimmers think this is a big deal because they can only increase their respiration rate by increasing their stroke rate, which will require more energy and O2, which will increase their breathing, which will increase their stroke rate….ok you get it.
Tangent: High body temp will also increase breathing rate… increasing perceived exertion, another reason hot pools are more painful to train in.
You might think you can fix problem of air hunger by training your lungs to increase their size and capacity. Sorry…not possible. The size of your lungs are fixed, the number of alveoli are fixed and there is nothing you can do about it. But what you can train is how sensitive those nerves are that control breathing. See, your body is a little sensitive to changes in CO2 which is what gives you that “take a breath NOW” feeling. But the more you expose your body to that feeling through breathe control exercises, the less those nerves react, and the more comfortable you feel when holding your breath. This does not change O2 levels in the body…so you will still pass out at the same time.
Speaking of passing out… hyperventilating before a “swim as far as you can underwater” challenge is a bad idea because of what we talked about. Because breathing is first controlled by CO2 levels, hyperventilation will decrease CO2 in the body and will make you feel very comfortable when you hold your breath. BUT…O2 is still going to run out at the same time and you won’t have that “you need to breathe” sensation to tell you when to come up. So you end up passing out underwater when your brain runs out of O2, and that is when coach dives in.
What about hyperventilation before a race? I think there are enough other signals telling you to breathe during a race that it is ok to hyperventilation before a race in order to make it easier to hold your breath. But remember, holding your breath decreases heart function since your body wants to conserve O2 to keep your brain and heart happy. So unless you are sprinting the 50… holding your breath is a bad idea in general for a swimmer.
Dealing with acid: the connection between lactate and CO2
We keep saying lactic acid is basically CO2 which is basically in control of pH… now it is time to take a closer look. Let us start with what we know. CO2 is created in the mitochondria during the Krebs cycle when burning sugar or fat (refer to Energy Systems). This CO2 is like garbage to the cell and needs to be taken out. The cell dumps its CO2 into the blood where this happens:
CO2 goes from the muscle cell into the red blood cell where it is converted into carbonic acid and then bicarbonate (shifting from left to right on the equation). The more CO2 we make, the more the equation will run from left to right: decreasing CO2, creating more acid and lowering pH. Bicarbonate is a buffer, and will “eat up” the acid and CO2 and acts like a transporter of CO2 (70% of CO2 is transported in the form of bicarbonate).
Tangent: 25% of CO2 transported directly by hemoglobin, 5% is dissolved directly in the blood.
When the blood is pumped to the lungs, the whole sequence reverses, creating more CO2, decreasing acid and raising pH. The extra CO2 is now put into the alveoli and breathed out. Yay!
Tangent: This is how weight loss works. You breathe the weight off…weird.
That’s all fine and dandy if all we had to worry about is CO2 from burning sugar and fat, but we also have to deal with lactic acid. Any acid, if you remember from chemistry class, is simply the amount of hydrogen atoms floating around. Lactic acid can be thought of as dumping pure hydrogen atoms into the blood, which is the right side of the equation. This extra hydrogen is buffered by the bicarbonate in the blood, which keeps your pH in a nice happy area.
But do you remember titrating acid into a buffer in chemistry class? Everything is ok until it’s not. You keep adding acid one drop at a time, and the buffer eats it up no problem. Then, all of a sudden you add one more drop and the whole color of your liquid changes because you ran out of buffer. The same thing happens in your body. Lactic acid and hydrogen are buffered just fine, but then all of a sudden it’s too much and that is when you hit the wall. We have all felt this before, the race is going just fine, and then all of a sudden everything falls apart. This is why that happens.
Since we added a whole bunch of hydrogen on the right side of the equation, everything gets shifted to the left side. That means more CO2. This is called “non-metabolic CO2” which means that it came from the buffering system in the blood, and not from burning sugar and fat. This is why lactic acid = CO2 and why you feel like you need to breathe so much during a sprint race even though you are not using O2. Just remember, the buffer won’t last forever, and the more CO2 you can get rid of, the longer the buffer will last. So in races longer than say…40 seconds, you need to breathe a lot and stay ahead of the acid building up as much as possible. That’s why coach says “breathe early and breathe often” before your 200s.
Tangent: Between breathing deeper and faster, breathing can increase 32x from rest…use that!
I know that is really confusing… but the big picture is this: lactic acid = CO2. CO2 only leaves the body by breathing out, so the more you breathe, the more you get rid of acid.
One more interesting thing to know, even at the highest intensity of workout athletes can still voluntarily increase their breathing. That means even at the highest intensity, your lungs can still function at a higher level and they are not the limiting factor in your performance. BUT, that was discovered in runners who, once again, can breathe whenever they want. I wonder if you would find the same thing in swimmers… are we limited by our ability to breath in the water, or are we just that awesome?
Tangent: Because of the new CO2 being made by lactic acid from glycolysis, you can actually measure how much of each system (glycolysis vs. aerobic) you are using just be comparing CO2 and O2 breathed in and out. This is called RER… respiratory exchange ratio.
Lung capacity: Why do we train so much breathe control if you can't change the size of your lungs?
We said earlier that you can’t change the size of your lungs, so why does coach bother making me do all these breathe control sets? That’s because we also said that breathing is performed by muscles, and just like any other muscle these can get tired, weaken and limit our ability. You can test this right now. Breathe as fast and as deep as you can for a minute. You will notice that you were able to do it more easily and better at the beginning than at the end of that minute. You may not feel the acid build up and burn like it does in your quads during a kick set, but it is happening all the same.
Since breathing in requires a contraction of the muscles, which is when you will be training them the most. So holding your breathe is like performing a constant contraction and will train those muscles to develop better capillaries, more mitochondria and better efficiency just like any other trained muscles. The same goes for breathing through a small hole, like a half closed snorkel. The extra effort it takes to suck in the air helps build those muscles, making breathing easier and more efficient during a race.
Practicing breathing for a swimmer is even more important than for any other athlete because we are given a limited amount of opportunities and time to breathe during a race. That means we need to make the most of each breath. Breathe timing to a swimmer becomes part of their stroke’s motor pattern (the muscle memory that takes over during a race). Practicing drills with breathing during workout helps improve and maximize the effect of each breath. This gives your body the best supply of O2 and best disposal of CO2 it can get, maximizing your performance overall and helping you beat that kid next to you.
Remember, being fast in the water is about working with the water and your stroke. The more comfortable you are, the more you can push the limit and go faster. Simply trying to “push through it” all the time will eventually hit its limit, and then you will have to “think through it” and control your body in order to take advantage of biology and physics in the water. That’s why training smart (and your lungs) is just as important as training hard.