"I Can't Catch My Breath": Lungs And Distance Running Performance

By Jason R. Karp, M.S.

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    Jason Karp tackles another subject for Track Coach-The mechanism of breathing and oxygen transport in connection with distance running. It is helpful for every coach to understand precisely what is happening in this process.

    Air is fascinating. You can't see it, taste it, smell it, hear it, or feel it when it is still. Believe me, I've tried. But air seems to escape all of our senses. Most of the time, we don't even think about air, except maybe when we travel on an airplane, or when a strong wind---in effect, moving air---blows in our face as we walk outside.
    And then, of course, there's running. We think about air then, since we can certainly hear our in- creased breathing, and since many new runners seem to complain that they can't breathe once they start running around the block. Indeed, "getting in enough air" is foremost on their minds.
    I used to coach an accomplished runner who grunted during intense workouts or races, as if to get in, or get out, more air. It's a marvel of physiology (what scientists call diffusion) that enough air gets into our bodies, with our air holes---nostrils---being no larger than the size of a pea. (I know some people who have so much hair in their nostrils it's a wonder how any air gets through. )
    What is of greater interest is how the amount of air that we breathe increases by so much when we run. Ventilation, the movement of air in and out of the lungs, increases linearly at slow running speeds but increases exponentially at faster speeds, when there is an increased need to eliminate the metabolic production of carbon dioxide.
    This increase in ventilation is mediated by an initial increase in tidal volume (the amount of air in a single breath) at slower speeds and an increase in breathing frequency at faster speeds. It is not uncommon for a large male, who at rest breathes about half a liter of air per breath and about six liters per minute, to breathe nearly 200 liters per minute while running as hard as he can. That's 53 gallons of air entering the lungs each minute! Go to the supermarket and buy 53 gallons of milk, and then think of trying to drink those 53 gallons in one minute. Makes you have a lot more respect for the lungs.
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    Those newcomers to the sport of running seem to get frustrated with their lungs, because they perceive them to limit their ability to continue running. However, studies clearly show that the lungs do not limit the ability to perform endurance exercise, especially in untrained people.
    That limitation rests on the shoulders of the cardiovascular and metabolic systems, with blood flow to and oxygen use by the muscles the major culprits. However, it is precisely these people, the newcomers to the sport of running, who claim that they "can't breathe" while running and are forced to stop so that they can "catch their breath." Even trained runners sometimes feel this way.



    At first glance, distance running seems to have everything to do with big, strong lungs. After all, it is through our lungs that we get oxygen. If the size of our lungs mattered, you would expect the best distance runners to have large lungs that can hold a lot of oxygen. However, the best distance runners in the world are quite small people, with characteristically small lungs.

    Total lung capacity, the maximal amount of air the lungs can hold, is primarily influenced by body size, with bigger people having larger lung capacities. There is no relationship between lung capacity and distance running performance.
    Trying to breathe more deeply in an attempt to get in more oxygen will not make you run faster because getting more oxygen into your body is not what limits your ability to run. Oxygen is all around us and has no problem diffusing from the air into our lungs (despite our pea-sized nostrils).
    What is important in the lungs, however, is the process of oxygen diffusion from the alveoli of the lungs into the pulmonary capillaries. The pulmonary capillaries feed into the left side of the heart, which is responsible for pumping blood and oxygen to your organs, including your running muscles. This elegant process of diffusion is already more than adequate, even when running at racing speeds.



    The adequacy of oxygen transport from the lungs into the blood is elucidated by the often-presented oxyhemoglobin dissociation curve like the one shown in Figure 1. Oxygen saturation of arterial blood is affected by the pressure oxygen exerts in the arteries (called the oxygen partial pressure).

    While you sit reading this (at sea level), the hemoglobin in your arterial blood is 97-98% saturated with oxygen and your oxygen partial pressure is about 100 millimeters of mercury (mmHg). Even while running a race, this near-maximal saturation is maintained in healthy people.
    As the graph below shows, the curve is nearly flat at high partial pressures, so a slight reduction in partial pressure does not have a significant effect on arterial oxygen saturation. However, if the oxygen partial pressure decreases below approximately 70 mmHg, arterial oxygen saturation begins to decrease rapidly.
    This latter situation only hap- pens at very high altitudes, in patients with cardiovascular or pulmonary pathology, and in some elite endurance athletes who exhibit a condition known as exercise-induced hypoxemia.



    Unlike the cardiovascular and muscular systems, the pulmonary system, including the lungs, is believed to not adapt to training. Therefore, the lungs may limit performance in elite endurance athletes who have developed the more trainable characteristics of aerobic metabolism (e.g., cardiac output, hemoglobin concentration, and mitochondrial and capillary volumes) to capacities that approach the genetic potential of the lungs to provide for adequate diffusion of oxygen. In other words, the lungs may limit performance by "lagging behind" other, more readily adaptable characteristics. But this is only a problem when those other characteristics have been trained enough to reach their genetic potential.



    Sometimes, the level of work that elite endurance athletes can do places too high a demand on the cardiopulmonary system to supply the necessary oxygen to sustain the work. One of the major pulmonary issues of elite endurance athletes, who have excessively high metabolic and thus ventilatory demands, is the high oxygen cost associated with that ventilation, representing a potentially significant "steal" of blood flow from the main exercising muscles.
    During moderate running (e.g., 70% maximal oxygen consumption, or VO2max), the oxygen cost of ventilation is approximately 3-6% of total body oxygen consumption, while during maximal running, it is about 10% of VO2max, costing as much as 13-15% in some athletes. So, not only will taking deeper breaths not get more oxygen into your blood, the extra muscle action necessary for a larger inspiration may take away some of the oxygen that is needed by your leg muscles.
    So next time you're running up a hill or finishing an interval workout on the track and you're thinking, "I can't catch my breath," don't blame your lungs.




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Jason R. Karp is a Ph.D. candidate in exercise physiology at Indiana University. A competitive runner who does not blame his lungs for his legs not running faster, he is a professional certified running coach and free-lance writer. His writing has appeared in numerous national running, coaching, and fitness magazines. He currently coaches athletes of all abilities through RunCoachJason.com. E-mail him at j ason@runcoachjason.com.


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