Air is fascinating. You can’t see it, taste it, smell it, hear it, or feel it when it is still , 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 blows in our face when we walk outside.

But then there is running, we think about air then. We can certainly hear our increased breathing and many new runners seem to complain that they can’t breathe once they start running around the block – ‘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 nostrils being no larger than the size of a pea. What is of greater interest is how the amount of air that we breathe increases by so much when we run. ‘

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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’s not uncommon for a large male who at rest breathes about half a litre of air per breath and about six litres of air per minute, to breathe nearly 200 litres per minute while running as hard as he can!

Go to the supermarket and buy 200 litres of milk and then try to drink those 200 litres in one minute. Makes you have a lot more respect for the lungs. Running newcomers seem to get frustrated with their lungs, because they perceive them to limit their ability to continue running. However, research shows 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’s the newcomers 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.

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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 how fast you run a 10K. Our main stimulus to breathe (at sea-level) is an increase in blood’s carbon dioxide content.

You breathe more during fasterpaced workouts and races not because you need more oxygen, but because more carbon dioxide is being produced in your muscles and needs to be expelled through the lungs. Oxygen is all around us and has no problem diffusing from the air into our lungs (despite our pea-sized nostrils).

The situation is slightly different at altitude, where you breathe more to compensate for your blood being less saturated with oxygen. Coaches often tell their athletes to breathe deeply, to take in more oxygen. But since your blood is already saturated with oxygen, it’s fruitless to take deeper breaths.

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. Furthermore, since your diaphragm and other breathing muscles also must use oxygen while you run, the extra muscle contractions needed to take deeper breaths may steal some of the oxygen needed by your leg muscles.

What is important in the lungs 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 process of diffusion is already more than adequate – at sea level your blood is nearly 100 percent saturated with oxygen, both at rest and even while running a race. The adequacy of oxygen transport from the lungs into the blood is shown by the ‘oxyhemoglobin dissociation curve’ as shown – see Fig 1.

Oxygen saturation of arterial blood is affected by the pressure oxygen exerts in the arteries (called ‘oxygen partial pressure’). While you sit reading this (at sealevel), the hemoglobin in your arterial blood is 97 to 98 percent 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 Fig 1 displays, 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 only happens 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 (a decrease in blood oxygen saturation during intense exercise). Unlike the cardiovascular and muscular systems, the pulmonary system does not adapt to training.

Therefore, the lungs may limit performance in elite endurance athletes who have developed the more trainable characteristics of aerobic metabolism, for example, cardiac output, hemoglobin concentration and the density of mitochondria (your aerobic factories that regenerate energy for muscle contraction) and capillaries (small blood vessels that perfuse your muscle fibres) 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.

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Strategies to enhance cardiovascular and metabolic performance to help you breathe easier

Run Intervals

Aterial Saturation (%) Interval training increases your heart’s ability to pump blood and oxygen to your muscles and increases your VO2max (the maximum amount of oxygen your muscles consume; measured in millilitres of oxygen per kilogramme of body weight per minute). Try this workout: I 4-5 x 3-4min @ VO2max pace (2K3K race pace, 95-100% max heart rate) with 3-4 min jog recovery

Run Longer

Running longer increases the storage of fuel in your muscles (in particular carbohydrates), improving your endurance. Increase your weekly long run by 2 kilometres each week.

Run More

Running more kilometres per week enhances your blood vessels’ oxygencarrying capability by increasing blood volume. It also creates a larger capillary network perfusing your muscle fibres, providing more oxygen to your muscles and increases muscles’ density of mitochondria, the microscopic ‘aerobic factories’ that use oxygen. Increase your weekly distance by about 10 percent every 3 weeks by adding 1 to 2 kilometres to each day of running.

If getting more oxygen into your lungs doesn’t limit your ability to run faster, what does?

It’s all about getting more oxygen to your muscles. And you do that by increasing the performance of your cardiovascular and metabolic systems through relevant training (see panel), not by taking deeper breaths. There are a number of things you can do to improve cardiovascular and metabolic performance, including running intervals, running longer, and increasing your weekly running volume.

Training your cardiovascular and metabolic characteristics improves your ability to transport and use oxygen, making you feel less out of breath. 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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