Normobaric Hypoxia Exposure During Sleep Does Not Improve Time-Trial Performance In Hypobaric Hypoxia

This study determined if sleeping in normobaric hypoxia (NH) induces sufficient acclimatization to improve time‐trial (TT) performance in hypobaric hypoxia (HH). Two groups of sea‐level (SL) residents having similar peak oxygen uptakes (~47 ml/kg/min), ages (~24 yr), and weights (~75 kg) slept for ~6.5 hrs/night for 7 consecutive nights in portable rooms under blinded NH (n=14) or SL (n=8) conditions. Ambient % O 2 for the NH group was progressively reduced by ~0.30% O 2 each night from ~16.2% O 2 (2200 m equivalent) on the 1 st night to ~14.4% O 2 (3050 m) on the 7 th night. The SL group remained at =20.5% O 2 (150 m). Within 25 hrs of treatment end, all were exposed to HH (Pikes Peak, CO; 4300 m). At SL before treatment and in the first 5 hrs of HH, an all‐out, 7‐mile treadmill TT was performed. Volunteers freely adjusted speed but grade was fixed at 3%. Heart rate (HR) and oxygen saturation (SaO 2 ) were recorded every 5 min. For both groups, TT duration increased (P<0.01) while HR and SaO 2 decreased (P<0.02) from SL to HH. There were no between‐group differences at SL or HH for TT duration (SL: 75±4 vs 73±4 min; HH: 103±6 vs 106±6 min), HR (SL: 165±2 vs 168±5 b/min; HH: 154±1 vs 150±3 b/min) or SaO 2 (SL: 95±1 vs 96±1; HH: 74±1 vs 73±2). These results indicate that sleeping 7 nights in NH did not induce sufficient acclimatization to improve TT performance in HH. Funding: US Army MRMC ATO IV.MD.2006.01. Authors' views; not official U.S. Army or DoD policy.