Effects of Exercise Training in Hypoxia Versus Normoxia on Vascular Health.
BACKGROUND
Exercise training (ExT) prompts multiple beneficial adaptations associated with vascular health, such as increases in skeletal muscle capillarization and vascular dilator function and decreases in arterial stiffness. However, whether ExT performed in hypoxic conditions induces enhanced effects is unclear.


OBJECTIVE
We sought to systematically review the literature and determine whether hypoxic ExT leads to superior vascular adaptations compared with normoxic ExT.


METHODS
We searched MEDLINE, Scopus, and Web of Science from their inception until September 2015 for articles assessing vascular adaptations to ExT performed under hypoxic and normoxic conditions. We performed meta-analyses to determine the standardized mean difference (SMD) between the effects of ExT performed in hypoxia versus normoxia on vascular adaptations. We assessed heterogeneity among studies using I2statistics and evaluated publication bias via the Begg and Mazumdar's rank correlation test and Egger's regression test.


RESULTS
After systematic review, we included 21 controlled studies, including a total of 331 individuals (mean age 19-57 years, 265 males). ExT programs primarily consisted of cycling endurance training performed in normobaric hypoxia or normoxia; duration ranged from 3 to 10 weeks. The exercise intensity was similar in relative terms in the groups trained in hypoxia and normoxia in the majority of studies (17 of 21). After data pooling, skeletal muscle capillarization (n = 182, SMD = 0.40, 95 % confidence interval [CI] 0.10-0.70; P = 0.01) and vascular dilator function (n = 71, SMD = 0.67, 95 % CI 0.17-1.18; P = 0.009) but not arterial stiffness (n = 112, SMD = -0.03, 95 % CI -0.69 to 0.63; P = 0.93), were enhanced with ExT performed in hypoxia versus normoxia. We only found heterogeneity among studies assessing arterial stiffness (I2= 63 %, P = 0.02), and no publication bias was detected.


CONCLUSIONS
Based on current published studies, hypoxic ExT potentiates vascular adaptations related to skeletal muscle capillarization and dilator function. These findings may contribute to establishing effective exercise programs designed to enhance vascular health.
Institute of Physiology, ZIHP, University of Zurich, Office 23 J 64, Winterthurerstrasse 190, 8057, Zurich, Switzerland. david.montero.barril@gmail.com.
David
D
Montero
Institute of Physiology, ZIHP, University of Zurich, Office 23 J 64, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
Carsten
C
Lundby
D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D015444:Exercise / Q000502:physiology*; D006801:Humans; D000860:Hypoxia; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D010101:Oxygen Consumption; D059289:Vascular Stiffness; D055815:Young Adult