title: Mechanisms of Improved Exercise Performance under Hyperoxia.
abstract: BACKGROUND
  The impact of hyperoxia on exercise limitation is still incompletely understood.
  
  
  OBJECTIVE
  We investigated to which extent breathing hyperoxia enhances the exercise performance of healthy subjects and which physiologic mechanisms are involved.
  
  
  METHODS
  A total of 32 healthy volunteers (43 ± 15 years, 12 women) performed 4 bicycle exercise tests to exhaustion with ramp and constant-load protocols (at 75% of the maximal workload [Wmax] on FiO2 0.21) on separate occasions while breathing ambient (FiO2 0.21) or oxygen-enriched air (FiO2 0.50) in a random, blinded order. Workload, endurance, gas exchange, pulse oximetry (SpO2), and cerebral (CTO) and quadriceps muscle tissue oxygenation (QMTO) were measured.
  
  
  RESULTS
  During the final 15 s of ramp exercising with FiO2 0.50, Wmax (mean ± SD 270 ± 80 W), SpO2 (99 ± 1%), and CTO (67 ± 9%) were higher and the Borg CR10 Scale dyspnea score was lower (4.8 ± 2.2) than the corresponding values with FiO2 0.21 (Wmax 257 ± 76 W, SpO2 96 ± 3%, CTO 61 ± 9%, and Borg CR10 Scale dyspnea score 5.7 ± 2.6, p < 0.05, all comparisons). In constant-load exercising with FiO2 0.50, endurance was longer than with FiO2 0.21 (16 min 22 s ± 7 min 39 s vs. 10 min 47 s ± 5 min 58 s). With FiO2 0.50, SpO2 (99 ± 0%) and QMTO (69 ± 8%) were higher than the corresponding isotime values to end-exercise with FiO2 0.21 (SpO2 96 ± 4%, QMTO 66 ± 9%), while minute ventilation was lower in hyperoxia (82 ± 18 vs. 93 ± 23 L/min, p < 0.05, all comparisons).
  
  
  CONCLUSIONS
  In healthy subjects, hyperoxia increased maximal power output and endurance. It improved arterial, cerebral, and muscle tissue oxygenation, while minute ventilation and dyspnea perception were reduced. The findings suggest that hyperoxia enhanced cycling performance through a more efficient pulmonary gas exchange and a greater availability of oxygen to muscles and the brain (cerebral motor and sensory neurons).
authors.affiliation: Pulmonary Clinic, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Silvia
authors.initials: S
authors.lastname: Ulrich
authors.forename: Elisabeth D
authors.initials: ED
authors.lastname: Hasler
authors.forename: Séverine
authors.initials: S
authors.lastname: Müller-Mottet
authors.forename: Stephan
authors.initials: S
authors.lastname: Keusch
authors.forename: Michael
authors.initials: M
authors.lastname: Furian
authors.forename: Tsogyal D
authors.initials: TD
authors.lastname: Latshang
authors.forename: Simon
authors.initials: S
authors.lastname: Schneider
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Saxer
authors.forename: Konrad E
authors.initials: KE
authors.lastname: Bloch
mesh_terms: D000328:Adult; D054022:Cerebrum / Q000378:metabolism*; D018592:Cross-Over Studies; D015444:Exercise; D005080:Exercise Test; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D018496:Hyperoxia / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010807:Physical Endurance; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation; D052097:Quadriceps Muscle / Q000378:metabolism*; D016526:Workload