Breathing variability during running in athletes: The role of sex, exercise intensity and breathing reserve

Highly trained aerobic athletes progressively use most of their breathing reserve with increased exercise intensity during whole-body exercise. Additionally, females typically present proportionally smaller lungs than males. Therefore, sex, exercise intensity, and breathing reserve use likely influence the volume and time in which respiratory parameters vary between consecutive breaths during whole-body exercise. However, breath-by-breath variability has been scarcely investigated during exercise. Accordingly, we sought to investigate breath-by-breath pulmonary ventilation (V̇_E), tidal volume ₍V_T), and respiratory frequency (f_R) variability during a maximal treadmill incremental exercise test in 17 females and 18 males highly trained professional endurance runners. The breath-by-breath variability was analyzed by root mean square of successive differences (RMSSD) within 1-minute windows. Females had lower absolute and percent predicted forced expiratory volume in one second (FEV₁) and forced vital capacity (FVC) than males, as well as lower height-adjusted absolute FVC than males. V̇_E and V_T reserve use were similar between the sexes at peak exercise. While RMSSDV̇_E and RMSSDf_R did not change over exercise (P > 0.05), RMSSDV_T progressively decreased (P < 0.001). RMSSDV_T was negatively correlated with V_T reserve use only in males. Females showed lower RMSSDV̇_E than males during the entire exercise test (P < 0.001). At iso-V̇_E reserve use, between-sex differences in RMSSDV̇_E persisted (P = 0.003). Our findings indicate that exercise intensity decreases V_T variability in professional runners, which is linked to V_T reserve use in males but not females. Additionally, the female sex lowers V̇_E variability regardless of exercise intensity and V̇_E reserve use.