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

Abstract

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. This multicentre international study used cardiac MRI and cardiopulmonary exercise testing (VO₂peak) to assess sex-specific relationships between measures of biventricular chamber size, function, fibrosis and VO₂peak. Of the 364 endurance athletes included, 36.5% were female. Compared with males, female athletes achieved lower VO₂peak (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 VO₂peak (r=0.60-0.66) and a similar coefficient describing the linear relationship between VO₂peak and LVEDV (Females: VO₂peak(mL/min)=12.1×LVEDV+963.9; males: VO₂peak=15.3×LVEDV+806.8, p=0.100) and BSA-indexed LVEDV (females: VO₂peak (mL/kg/min)=0.37×LVEDV/BSA+12.5; males: VO₂peak=0.51×LVEDV/BSA-1.2, p=0.059). There was no difference between right ventricular (RV) measures and VO₂peak; 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). 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.