Among the many physical parameters that it is useful to know and that help us better understand our bodies and improve them through physical activity, blood oxygenation level is one of the “newest.” Not because it is in an absolute sense: in the medical field, in fact, the percentage of oxygen in the blood is a factor that has been constantly monitored for a very long time, since it is linked to parameters of well-being or discomfort: for simplicity’s sake, suffice it to know that the higher the oxygenation, the better the state of health and vice versa.
Its monitoring has been made easier in recent years because it can be done even without medical help thanks to simple instruments called pulse oximeters (a kind of clip with which to staple the index finger) that in no time, thanks to the use of an infrared light, can optically read this parameter by observing the refraction of oxygen in the blood.
For some time, some sportwatch models have also had this function, and as we will find out in a moment, there is a specific reason for it, besides the obvious one of providing an important parameter.
What is the purpose of blood oxygenation and why is it important to monitor it?
Oxygen binds in the blood to hemoglobin and functions like “cars” on a train, transporting it to muscle tissues. Here is-very simply-explained why it is important that your blood is adequately oxygenated: the better it is, the better the conditions in which your muscles will operate, being able to rely on the fullest supplies of energy to endure and overcome exertion.
An average adult individual needs 550 liters of oxygen per day. Under mild to moderate physical activity, the percentage of oxygen in the blood does not change appreciably. During intense activity, on the other hand, this parameter drops and it is correct to keep it under control. The same happens to trail runners, especially those who train and race at high altitudes: in fact, it is well known that as the percentage of oxygen in the air decreases as altitude increases, the percentage of oxygen in the blood also decreases, subjecting the muscular system to additional strain. It is precisely this particular “environmental” condition that is exploited, as we shall see, by ultratrail runners to work on and improve their endurance, as Kilian Jornet recounted in a recent interview with The Extramilest Show podcast.
The blood oxygenation value provided by the pulse oximeter is called Sp02, and the ranges in which it varies are called normal or low depending on the percentage detected: between 95 and 100 oxygenation is normal, while below that threshold and up to 90 indicates a condition of mild or pronounced oxygen deficiency called “hypoxemia.”
Now that you know your blood oxygen percentage, what can you do about it? Here are some practical cases. Always keep in mind that this parameter varies much more slowly than the heart rate, so its readings provide indications to be interpreted (and possibly corrected) by acting more upstream and less immediately. In short, it is not a matter of varying the running pace :)
When you are recovering
Blood oxygen saturation can provide important training (or recovery) cues for athletes. Let’s say you are following a training program but at the same time you are feeling more tired than usual. If your saturation is below average, it is important to modify your training plan by introducing a recovery day or two instead of insisting on physical exertion, which could further impair your physical condition. Most likely your exhaustion is due to external factors or insufficient recovery due to difficulty sleeping: stopping and resting is the solution, and the pulse oximeter can help you decide, removing any doubt.
As mentioned earlier, at high altitude the percentage of oxygen in the air is lower than at sea level. At the latter elevation it is in fact 21% while above 3000 meters it drops to 15%. With what consequences? More fatigue to train and endure physical exertion, mainly, but also some advantages, so much so that not only trail runners but also “road” athletes train at altitude.
What is involved in altitude training and saturation reduction? That the heart and breathing will increase in frequency and the volume of plasma pumped will increase to make up for the lack of oxygen and still carry as much as possible to the muscles. The most immediate physical result is not the most exciting: fatigue and training below the usual threshold, so much so that in the first few days at altitude it is reasonable to decrease the workload.
It is after that, however, that something happens. The more the body adapts, the more the production of red blood cells and the volume of hemoglobin increases, until after about 4 weeks (but as early as the second week onward) breathing and heart rate stabilize. What does it mean once you return to run on your usual streets? That your heart will be working at normal rates but carrying more oxygen-rich blood, allowing you a kind of extra gear at normal rates. In short, if you were a car, it is as if you could use a higher-performance fuel that makes you run harder, without making your engine run faster. For the same amount of effort, in other words, you would get better performance.
It should also be mentioned that these positive changes in performance are not common to all athletes and that benefits on flat surfaces have a variable but not infinite duration, so much so that professional athletes-especially in cycling, running and trailrunning, and of course mountaineering-repeat training sessions at altitude every year.
Some trail runners-such as the aforementioned Kilian Jornet-follow training programs that include oxygen deprivation sessions. In the specific case, the purpose of lowering saturation is to increase endurance, especially at high altitudes (where they usually compete). Studies in this field-which also consider the use of apnea to increase hemoglobin in the blood-are still at a preliminary stage and, so far, do not appear to have demonstrated performance increases in endurance and speed but almost certainly in endurance in cold temperatures, a condition that may be of great interest to ultratrail runners.