Exercise Intensity and Circulating CD34+ Progenitor Cell Mobilization in Trained Adults

This randomized crossover study investigated whether exercise intensity influences the mobilization of circulating CD34+ progenitor cells when total external work is matched. Forty trained male endurance athletes completed two cycling exercise conditions in randomized order: a higher-intensity condition at 70% of peak work rate (WRpeak) and a lower-intensity condition at 30% WRpeak. Both conditions were performed until 250 kJ of external work had been completed and were separated by a washout period of at least 7 days. Venous blood samples were obtained before exercise, immediately after exercise, and at 15, 30, and 60 minutes of recovery. The primary outcome was the absolute concentration of viable circulating CD34+ cells measured using single-platform flow cytometry. Secondary outcomes included CD34+CD45dim, CD34+CD133+, and CD34+VEGFR2+ cell phenotypes, together with adrenergic, metabolic, chemokine, growth-factor, and cardiovascular responses. The study was designed to determine whether exercise intensity produces distinct progenitor-cell mobilization responses despite identical external work.