Female endurance athletes: smaller hearts but similar relationship between ventricular size, fitness and fibrosis as male athletes

Objectives Exercise-induced cardiac remodelling is well described in male athletes but incompletely understood in females. This study aimed to examine sex differences in cardiac structure, function and fibrosis relative to fitness and to determine reference ranges for ‘normal’ chamber size in a large cohort of healthy male and female highly trained endurance athletes. Methods This multicentre international study used cardiac MRI and cardiopulmonary exercise testing (VO 2 peak) to assess sex-specific relationships between measures of biventricular chamber size, function, fibrosis and VO 2 peak. Results Of the 364 endurance athletes included, 36.5% were female. Compared with males, female athletes achieved lower VO 2 peak (51 (40–57) vs 59 (41–65) mL/kg/min, p<0.001), had smaller absolute and body surface area (BSA)-indexed left and right end-diastolic volumes (LVEDV, respectively) but similar volumes when indexed to fat-free mass. Both sexes showed a strong association between LVEDV and VO 2 peak (r=0.60–0.66) and a similar coefficient describing the linear relationship between VO 2 peak and LVEDV (Females: VO 2 peak(mL/min)=12.1×LVEDV+963.9; males: VO 2 peak=15.3×LVEDV+806.8, p=0.100) and BSA-indexed LVEDV (females: VO 2 peak (mL/kg/min)=0.37×LVEDV/BSA+12.5; males: VO 2 peak=0.51×LVEDV/BSA-1.2, p=0.059). There was no difference between right ventricular (RV) measures and VO 2 peak; however, males had 3.8 times higher odds of reduced RV ejection fraction. Prevalent myocardial scar was similar for both female (14.2%) and male (19.9%) athletes (p=0.180). Conclusions Female and male athletes demonstrate similar cardiac remodelling relative to fitness and no sex difference in myocardial scar. The female athlete’s heart can show profound adaptation, and previous assertions that female hearts have lesser capacity for remodelling should be reappraised.