title: Multiple variables explain the variability in the decrement in VO2max during acute hypobaric hypoxia.
abstract: OBJECTIVE
  We used multiple regression analyses to determine the relationships between the decrement in sea level (SL, 760 Torr) VO2max during hypobaric hypoxia (HH) and variables that could alter or be related to the decrement in VO2max.
  
  
  METHODS
  HH conditions consisted of 682 Torr, 632 Torr, and 566 Torr, and the measured independent variables were SL-VO2max, SL lactate threshold (SL-LT), the change in hemoglobin saturation at VO2max between 760 and 566 Torr (delta SaO2max), lean body mass (LBM), and gender. Male (N = 14) and female (N = 14) subjects of varied fitness, training status, and residential altitude (1,640-2,460 m) completed cycle ergometry tests of VO2max at each HH condition under randomized and single-blinded conditions.
  
  
  RESULTS
  VO2max decreased significantly from 760 Torr after 682 Torr (approximately 915 m) (3.5 +/- 0.9 to 3.4 +/- 0.8 L.min-1, P = 0.0003). Across all HH conditions, the slope of the relative decrement in VO2max (%VO2max) during HH was -9.2%/100 mm Hg (-8.1%/1000 m) with an initial decrease from 100% estimated to occur below 705 Torr (610 m). Step-wise multiple regression revealed that SL-VO2max, SL-LT, delta SaO2max, LBM, and gender each significantly combined to account for 89.03% of the variance in the decrement in VO2max (760-566 Torr) (P < 0.001).
  
  
  CONCLUSIONS
  Individuals who have a combination of a large SL-VO2max, a small SL-LT (VO2, L.min-1), greater reductions in delta SaO2max, a large LBM, and are male have the greatest decrement in VO2max during HH. The unique variance explanation afforded by SL-LT, LBM, and gender suggests that issues pertaining to oxygen diffusion within skeletal muscle may add to the explanation of between subjects variability in the decrement in VO2max during HH.
authors.affiliation: Johnson Center, University of New Mexico, Albuquerque 87131, USA. rrobergs@unm.edu
authors.forename: R A
authors.initials: RA
authors.lastname: Robergs
authors.forename: R
authors.initials: R
authors.lastname: Quintana
authors.forename: D L
authors.initials: DL
authors.lastname: Parker
authors.forename: C C
authors.initials: CC
authors.lastname: Frankel
mesh_terms: D000328:Adult; D000531:Altitude; D001274:Atmospheric Pressure; D001692:Biological Transport; D004058:Diffusion; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D000860:Hypoxia; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D012737:Sex Factors
chemical_list: D010100:Oxygen