Hypoventilation training, pioneered by Emil Zátopek, is a training method by which one first inhale, then exhale normally, then hold his breathe.
Wikipedia notes that hypoventilation training delays acidosis and thus delay on onset of fatigue, allowing one to improve performance during strenuous exertions of short to moderate durations.
However, what are the disadvantages or side-effects of hypoventilation training (besides physically demanding)?
Specifically, is engaging in long-term hypoventilation training hazardous to health?