stylistic:style_transfer, structural:scholar_edition, stylistic:tone
By cause

Intermittent hypoxic training induces mild generalized hypoxia for short periods as a training method to improve sporting performance. This is not considered a medical condition. Acute cerebral hypoxia leading to blackout can occur during freediving. This is a consequence of prolonged voluntary apnea underwater, and generally occurs in trained athletes in good health and good physical condition.