Sex differences in hemodynamic response to high-intensity interval exercise

Sex differences in the cardiorespiratory and hemodynamic response to exercise exist due to differences in heart size, blood volume, and hemoglobin mass, eliciting higher maximal oxygen uptake (VO2max) in men versus women. Data are equivocal whether sex differences in training responsiveness occur. This study investigated potential sex differences in the hemodynamic response (stroke volume (SV) and cardiac output (CO)) to high-intensity interval exercise (HIIE). Habitually active men (n = 15) and women (n = 13) underwent VO2max testing, followed by three HIIE sessions consisting of the 4 x 4, 10 x 1, and reduced exertion high-intensity training (REHIT), whose order was randomized. During exercise, oxygen uptake (VO2) and hemodynamic responses were determined. Results showed no sex difference in peak relative VO2 (p = 0.263), CO (p = 0.277), or SV (p = 0.116), although absolute values were higher in men (p < 0.05). Peak absolute (127.3 +/- 20.6 vs. 115.2 +/- 16.6 mL/beat, p = 0.004, d = 0.66) and relative SV (111.0 +/- 15.5 vs. 100.7 +/- 11.1% max, p = 0.005, d = 0.78) were higher with REHIT versus 4 x 4. No sex differences in mean relative VO2, CO, or SV occurred (p > 0.05). Data showed lower mean VO2 during REHIT versus 4 x 4 (59.3 +/- 6.8 vs. 65.8 +/- 5.8 %VO2max, p < 0.001, d = 1.05) and 10 x 1 (59.3 +/- 6.8 vs. 69.1 +/- 7.4 %VO2max, p < 0.001, d = 1.4). Mean CO was lower in REHIT than 10 x 1 (79.8 +/- 8.6 vs. 84.0 +/- 7.4% max, p = 0.012, d = 0.53). Previously reported differences in VO2max response to HIIE may not be due to unique hemodynamic responses.