Purpose: Sleeping in a hypoxic environment is becoming increasingly popular among athletes attempting to simulate a "live high, train low" training regime. The purpose of this study was to investigate the acute effects (one night) of sleeping in a normobaric hypoxic tent (NH) (PO2 = 110 mm Hg [almost equal to] 2500 m) upon markers of sleep physiology and quality, compared with sleep in a normal ambient environment (BL) (PO2 = 159 mm Hg [almost equal to] sea level) and sleep in a normobaric normoxic tent (NN) (PO2 = 159 mm Hg). Methods: Eight male recreational athletes (age 34.5 +/- 6.9 yr; stature 169.1 +/- 8.7 cm; mass 69.3 +/- 8.2 kg; VO2max 56.4 +/- 8.3 mL[middle dot]kg-1[middle dot]min-1) participated in the study using a randomized, double-blind crossover design. Polysomnographic studies were undertaken to measure sleep stages, arterial oxygen saturation (SpO2), heart rate (HR), and the Respiratory Disturbance Index (RDI). The Leeds Sleep Evaluation Questionnaire (LSEQ) was used to measure subjective sleep quality. Results: NH (89.9 +/- 4.8%) resulted in a significantly lower (P < 0.05) SpO2 compared with both BL (95.7 +/- 1.5%) and NN (93.5 +/- 4.0%). Heart rate was significantly higher (P < 0.05) in NH (51.5 +/- 7.6 beats[middle dot]min-1) compared with NN (48.3 +/- 6.9 beats[middle dot]min-1) but was similar versus BL (50.3 +/- 4.3 beats[middle dot]min-1). RDI (counts[middle dot]h-1) and RDI (total counts) were lowest in BL (3.5 +/- 2.5; 18.1 +/- 7.9) and highest in NH (36.8 +/- 42.7; 221.9 +/- 254.5). The difference in RDI (counts[middle dot]h-1 and total counts) between NH and BL was significant (P < 0.05). The LSEQ revealed that subjects' "behavior following waking" score was significantly (P < 0.05) lower in NH (40.9 +/- 9.2) compared with BL (52.3 +/- 8.3). Conclusion: This study presents evidence that sleep in a normobaric hypoxic tent at a simulated altitude of 2500 m may affect sleep parameters in some individuals. This type of analysis may be useful in the early identification of poorly responding individuals to simulated altitude environments.
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