This study evaluated the sleep quality of athletes in normobaric hypoxia at a simulated altitude of 2,000 m. Eight male athletes slept in normoxic condition (NC) and hypoxic conditions equivalent to those at 2,000-m altitude (HC). Polysomnographic recordings of sleep included the electroencephalogram (EEG), electrooculogram, chin surface electromyogram, and electrocardiogram. Thoracic and abdominal motion, nasal and oral airflow, and arterial blood oxygen saturation (Sa(O(2))) were also recorded. Standard visual sleep stage scoring and fast Fourier transformation analyses of the EEG were performed on 30-s epochs. Subjective sleepiness and urinary catecholamines were also monitored. Mean Sa(O(2)) decreased and respiratory disturbances increased with HC. The increase in respiratory disturbances was significant, but the increase was small and subclinical. The duration of slow-wave sleep (stage 3 and 4) and total delta power (<3 Hz) of the all-night non-rapid eye movement sleep EEG decreased for HC compared with NC. Subjective sleepiness and amounts of urinary catecholamines did not differ between the conditions. These results indicate that acute exposure to normobaric hypoxia equivalent to that at 2,000-m altitude decreased slow-wave sleep in athletes, but it did not change subjective sleepiness or amounts of urinary catecholamines.

The mechanisms underlying subcellular oxygen transport mediated by myoglobin (Mb) remain unclear. Recent evidence suggests that, in the myocardium, transverse diffusion of Mb is too slow to effectively supply oxygen to meet the immediate mitochondrial oxygen demands at the onset of muscle contractions. The cell may accommodate the demand by maintaining the distribution of Mb to ensure a sufficient O(2) supply in the immediate vicinity of the mitochondria. The present study has verified the co-localization of Mb with mitochondria by using biochemical histological and electron microscopy analyses. Immunohistochemical and electron microscopy analysis indicates a co-localization of Mb with mitochondria. Western blotting confirms the presence of Mb colocalizes with the mitochondrial fraction and appears more prominently in slow-twitch oxidative than in fast-twitch glycolytic muscle. In particular, Mb interacts with cytochrome c oxidase-subunit IV. These results suggest that a direct Mb-mediated O2 delivery to the mitochondria, which may play a potentially significant role for respiration.

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