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, η²_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.

Figure 1

Peak oxygen uptake (V̇O_2peak) before and after 12 wk of SIT. Mean (bars), standard deviation (error bars), and individual (connecting lines) data are presented. *p < 0.05, main effect of time.

Figure 2

Change in peak cardiac output (Q̇_peak) for each participant. Open and shaded bars represent the female and male participants, respectfully. Diagonal patterned bars represent participants from our previous study and clear bars represent participants from the current study. The typical error (TE) for the measurement of Q̇_peak (i.e., ± 1.0 L/min) is indicated by the red shaded area.

Figure 3

Peak cardiac output (Q̇_peak; A) and peak arteriovenous oxygen difference (peak a-vO_2diff; B) before and after 12 wk of SIT. Mean (bars), standard deviation (error bars), and individual (connecting lines) data are presented. *p < 0.05, main effect of time.

Figure 4

Change in plasma volume (PV; A), hematocrit (Hct; B) and hemoglobin concentration ([Hb]; C) before and after 4 and 12 wk of SIT. Mean (bars) and standard deviation (error bars) are presented. *p < 0.05 between sexes at same time point (ǂ = sex × time interaction).

Figure 5

Study overview.