Since the middle of the 2000s, a series of studies has been conducted by French researchers of Paris 13 University to propose a new approach to hypoventilation training. Xavier Woorons and his team hypothesized that if breath holdings were carried out with the lungs half-full of air, rather than full of air as performed so far, it would be possible to significantly reduce body oxygenation. The results that were published confirmed the hypotheses. They demonstrated that through hypoventilation at low lung volume, that is the exhale-hold technique, it was possible, without leaving sea level, to decrease O2 concentrations in the blood and in the muscles at levels corresponding to altitudes above 2000 m.