Transthoracic Echocardiographic Reference Values in Male Professional Major League Soccer Players Under 21 Years of Age

OBJECTIVE: To define sport-specific echocardiographic reference values in elite male soccer players <21 years of age. BACKGROUND: Exercise-induced cardiac remodeling varies by sport and demographic factors. The use of general population reference values may lead to misclassification of physiological remodeling as pathology, particularly in young athletes. Normative echocardiographic data in elite adolescent soccer players remain limited. METHODS: We performed a cross-sectional echocardiographic analysis of 430 male Major League Soccer athletes on active rosters from 2018 to 2023. Standard echocardiographic parameters were assessed and compared with American Society of Echocardiography reference values. RESULTS: Athlete age ranged from 14 to 21 years (mean 18.8 years). The cohort was racially and ethnically diverse (28.6% Black, 33.0% Hispanic, 37.0% White). 29% of athletes had dilated left ventricular end-diastolic volume (> 74mL/m2), while right ventricular enlargement (>41 mm) was observed in 27.2%. Maximal left ventricular wall thickness ranged from 5.5 to 12.9 mm (mean 9.79 mm), with 43.0% of athletes demonstrating wall thickness >10 mm. Mean left ventricular mass index was 92.8 g/m CONCLUSION: In this large, racially diverse cohort of elite male soccer players under 21 years of age, we provide comprehensive sport-specific echocardiographic reference values that address critical gaps in adolescent and young adult male soccer players.