Hypoxic exercise training improves cardiac/muscular hemodynamics and is associated with modulated circulating progenitor cells in sedentary men

Background Circulating progenitor cells (CPCs) improve cardiovascular function and organ perfusion by enhancing the capacities of endothelial repair and neovasculogenesis. This study investigates whether exercise regimens with/without hypoxia affect cardiac and muscular hemodynamics by modulating CPCs and angiogenic factors. Methods Forty sedentary males were randomly divided into hypoxic (HT, n = 20) and normoxic (NT, n = 20) training groups. The subjects were trained on a bicycle ergometer at 60%VO_2max under 15% (HT) or 21% (NT) O₂ conditions for 30 min daily, five days weekly for five weeks. Results After the five-week interventions, the HT group exhibited a larger improvement in aerobic capacity than the NT group. Furthermore, the HT regimen (i) enhanced cardiac output (Q_H) and perfusion (Q _M)/oxygenation of vastus lateralis during exercise; (ii) increased levels of CD34⁺/KDR⁺/CD117⁺, CD34 ⁺/KDR⁺/CD133⁺, and CD34⁺/KDR ⁺/CD31⁺ cells in blood; (iii) promoted the proliferative capacity of these CPC subsets, and (iv) elevated plasma nitrite/nitrate, stromal cell-derived factor-1 (SDF-1), matrix metalloproteinase-9 (MMP-9), and vascular endothelial growth factor-A (VEGF-A) concentrations. Despite the lack of changes in Q_H and the number or proliferative capacity of CD34 ⁺/KDR⁺/CD117⁺ or CD34⁺/KDR ⁺/CD31⁺ cells, the NT regimen elevated both Q_M and plasma nitrite/nitrate levels and suppressed the shedding of endothelial cells (CD34^-/KDR⁺/phosphatidylserine⁺ cells). Conclusions The HT regimen improves cardiac and muscular hemodynamic adaptations, possibly by promoting the mobilization/function of CPCs and the production of angiogenic factors.