Biological sex does not influence the peak cardiac output response to twelve weeks of sprint interval training

Abstract Sprint interval training (SIT) increases peak oxygen uptake (V̇O 2peak ) but the mechanistic basis is unclear. We have reported that 12 wk of SIT increased V̇O 2peak and peak cardiac output (Q̇ peak ) and the changes in these variables were correlated. An exploratory analysis suggested that Q̇ peak increased in males but not females. The present study incorporated best practices to examine the potential influence of biological sex on the Q̇ peak response to SIT. Male and female participants (n = 10 each; 21 ± 4 y) performed 33 ± 2 sessions of SIT over 12 wk. Each 10-min session involved 3 × 20-s ‘all-out’ sprints on an ergometer. V̇O 2peak increased after SIT (3.16 ± 1.0 vs. 2.89 ± 1.0 L/min, η 2 p = 0.53, p < 0.001) with no sex × time interaction ( p = 0.61). Q̇ peak was unchanged after training (15.2 ± 3.3 vs. 15.1 ± 3.0 L/min, p = 0.85), in contrast to our previous study. The peak estimated arteriovenous oxygen difference increased after training (204 ± 30 vs. 187 ± 36 ml/L, p = 0.006). There was no effect of training or sex on measures of endothelial function. We conclude that 12 wk of SIT increases V̇O 2peak but the mechanistic basis remains unclear. The capacity of inert gas rebreathing to assess changes in Q̇ peak may be limited and invasive studies that use more direct measures are needed.