1. Please introduce yourself to the readers (how you started in the profession, education, credentials, experience, etc.).
My name is Xavier WOORONS, I am a PhD in Human Biology, specialized in exercise physiology, in particular in the physiological responses to hypoxia and hypoventilation (exercise and training). I’ve been working for 10 years in the laboratory “cellular and functional responses to hypoxia” of Paris 13 University.
In our recent article, we demonstrated that swimmers can really train under hypoxic conditions at sea level if they use a hypoventilation technique at low lung volume. The breathing technique consists of performing short breath holdings with the lungs half full of air. To do so, swimmers have to first exhale then hold their breath for a few seconds. This is called the"exhale-hold" technique. Using an innovative device that allows the continuous measurement of blood oxygenation, we have shown that the exhale-hold technique could lead to a drop in arterial oxygen saturation (SaO2) similar to what is generally recorded above 2000m.
3. What are some misconceptions in the swimming community about breath holding and hypoxia?
Since the early 1970’s, at the instigation of the American trainer James Counsilman, many swimmers have included in their training sessions exercises with restricted breathing. Generally, these exercises consist of swimming with fewer breaths relative to arm strokes (i.e. inhale every 5, 7, or 9 strokes instead of 2–3 strokes). This method has been called, and is still called by many coaches and swimmers, “hypoxic training”. However, this is misleading because so far, no study had ever demonstrated that reducing the breathing frequency during a swimming exercise could induce hypoxia. In fact, only a hypercapnic effect (higher CO2 concentrations) had been reported. In our research, we showed that swimmers cannot obtain a significant hypoxic effect when they use hypoventilation at high lung volume, that is when they hold their breath with the lungs full of air (inhalation then breath hold).
4. What were the main results of your study?
Our study brings several novelties:
1) For the first time, we have managed to continuously measure oxygen concentrations in exercising swimmers thanks to a waterproofed forehead sensor placed under the swimming cap and connected to an oximeter maintained out of the water. The former studies could assess O2 levels only after the exercise, either through a blood sampling or a digital or ear sensor. However, these kinds of measurements are not very reliable since SaO2 rapidly returns to normal levels (or close) after the exercise. The continuous measurement of SaO2 through a forehead sensor is interesting because it enables to explore new areas of research in swimming.
2) We showed that SaO2 could drop to 87% on average when swimmers used the exhale-hold technique. This level of SaO2 is generally recorded during moderate exercise performed at an altitude of about 2400m. On the other hand, SaO2 remained above 94% during the majority of exercise, when swimmers used the classical technique of hypoventilation applied since the 1970's (inhale-hold). This level of SaO2 cannot be considered as a hypoxic effect.
3) Performing hypoventilation with the exhale-hold technique led to a greater increase in lactate concentrations, and therefore a greater stimulation of anaerobic metabolism, than the exercise performed with normal breathing. Conversely, with the inhale-hold technique, lactate concentrations were lower than during exercise with normal breathing, thus reducing the stimulation of anaerobic metabolism.
5. What can coaches take from your research?
First, if coaches want their swimmers to really train under hypoxic conditions while remaining at sea level, they must replace the former hypoventilation technique (inhale-hold), used for about 40 years, by the hypoventilation technique at low lung volume (exhale-hold). After several weeks of hypoventilation training with the exhale-hold technique, the physiological adaptations that occur may delay fatigue and improve performance, as already shown in runners. Thus, swimmers may find an interest to include two or 3 times a week hypoventilation exercises over distances between 25 and 100m.
Second, coaches have to be aware that, through the exhale-hold technique, it is possible for swimmers to stimulate the anaerobic metabolism by using low or moderate exercise intensities. This could avoid to systematically using high speeds during training, which can be more traumatizing for the locomotor system. This feature could also be interesting for injured swimmers who must return progressively to their swimming activity. Using the exhale-hold technique, these swimmers could stimulate the anaerobic glycolysis without putting too much stress on their muscles, joints or tendons. Thus, this would allow them to return to a satisfactory level of performance more rapidly.
6. Can hypercapnea training also help swimmers?
At first sight, the effectiveness of hypercapnea training may be questionable. In fact, it appears that many coaches use this kind of training to increase the tolerance to hypercapnia in their swimmers and therefore to make them breathe less frequently during a race. Breathing less frequently could be interesting in swimming since each time you turn the head to inhale, hydrodynamic disturbances as well as discontinuity in propulsive actions occur. Consequently, drag and energy cost are greater. If swimmers are able to restrict their breathing during a race, they could reduce drag and thus save energy, which might, theoretically, improve performance by a few tenths of seconds.
However, I think that hypercapnia training may be interesting for another reason. Indeed, it is well known that high CO2 concentrations provoke acidosis in the body. After several sessions of hypercapnia training, physiological adaptations, such as better buffering capacity, may occur and allow reducing acidosis. My thesis is that this phenomenon can be exacerbated if you add the hypercpanic effect to the hypoxic effect, like when using the exhale-hold technique. Therefore, through hypoventilation training at low lung volume, swimmers could obtain strong physiological adaptations that may delay fatigue and finally improve performance.
7. Can hypoxic training help facilitate warm-up?
If you don't mind, I will call it hypoventilation training rather than hypoxic training considering the fact that there is a combined effect of hypoxia and hypercapnia. As I mentioned above, this kind of training elevates the level of acidity in the body and can therefore lead to fatigue. Consequently, I would not say that it can help facilitate warm-up. It could even be the contrary if hypoventilation is too strong.
However, hypercapnia and hypoxia also induce muscle vasodilatation, which can increase oxygen supply. As such, one could hypothesize that performing a light hypoventilation may improve warm-up.
In fact, I don't know the real effects because to my knowledge, no study has ever been published on this subject. This should be investigated in the near future.
8. One other question, there is a lot of research emerging of the benefits of inspiratory muscle training for swimmers. What do you think? Also, do you know of any practical methods of inspiratory training for those without equipment?
In swimming, the work of breathing is greater than in land-based sports because of the hydrostatic pressures. It is well known that swim training leads to large improvement in pulmonary function, and this, without inspiratory or, more generally, respiratory muscle training. However, during exhaustive exercise, it has been shown that inspiratory muscle fatigue occurs in some swimmers and over certain distances. Therefore, this could constitute a limiting factor to performance. In this case, I think that respiratory muscle training may be useful and may represent an ergogenic aid for swimmers.
In a recent study published by Lavin et al. (2013), it was hypothesized that limiting breath frequency during swimming could mimic the effects of respiratory muscle training. This assumption is based on the fact that hypoventilation during exercise further stresses the respiratory system through hypercapnia and mechanical loading. However, the results of the study showed no improvement in respiratory muscle function. Even though further studies are needed, I am not convinced that reducing the breathing frequency during training could represent an effective practical method for improving respiratory muscle strength without any equipment.
9. What research or projects are you currently working on or should we look from you in the future?
I will continue to work on hypoventilation training in the next few years. Currently, the project is to determine the effects of the exhale-hold technique on performance in swimmers. In the future, our goal is to find the optimal weekly training frequency of hypoventilation training, set intensity and set duration for improving performance in different sporting activities.
I would like to end this interview by saying that I have just published a book on hypoventilation training: "hypoventilation training, push your limits!". This book presents all the knowledge currently available on this training method and proposes tools for athletes who would like to include it in their training program. You can find all the information on this website: http://www.hypoventilation-training.com/
sports, swimming research has looked at many attributes of youth swimmers, including height, strength, and lean body mass. Dr. Barbosa has lead most of this research and discussed it on this website previously. 
