From Sedentary Individuals to Highly Trained Athletes: A Comprehensive Cardiovascular Magnetic Resonance Imaging Study of Cardiac Volumetry, Function, and Strain

BACKGROUND: Physiological remodeling of the athlete's heart can resemble certain cardiomyopathies, underscoring the importance of robust reference standards. However, most cardiac magnetic resonance imaging (CMR) based studies focus on a narrow subset of adult athletes, providing limited insight into the broader spectrum of exercise-induced changes. Here, we aimed to characterize volumetric, functional, and strain-based adaptations across varying physical activity levels, age groups, and sexes and to establish reference ranges. METHODS: We enrolled 656 participants (13-35 years) in a cardiovascular screening program at our tertiary center (2009-2020). We excluded individuals with cardiac disease, risk factors, or abnormal screening findings. Participants were categorized as sedentary (≤3hours/week), recreational (4-6hours/week), or highly trained (>6hours/week) athletes. CMR was performed using 1.5T scanners to assess ventricular and atrial volumes, myocardial mass, ejection fractions, and feature-tracking strain. We derived 95% prediction intervals stratified by age, sex, and training volume. RESULTS: Of the 575 healthy subjects, 390 were highly trained athletes (22±6 years, 64% male, 19±7 training hours/week), 102 recreational athletes (23±6 years, 60% male, 4±1 training hours/week), and 83 sedentary individuals (26±4 years, 42% male, 1±1 training hours/week). Increasing weekly training hours were associated with larger ventricular volumes, higher myocardial mass, lower ejection fractions, and strain. Compared to sedentary individuals, highly trained athletes had significantly larger left and right ventricular volumes (LVEDVi estimate 95% CI: 0.82 0.52-1.12, p<0.001), higher myocardial mass (LVMI 0.59 0.31-0.86, p<0.001), and increased left and right atrial volumes, even after adjusting for age, sex, and weekly training hours. We observed a non-uniform dose-response relationship across activity levels, with the most prominent cardiac adaptations occurring in highly trained athletes. Endurance athletes exhibited the most pronounced volumetric changes among the sport types. Finally, we derived stratified prediction intervals to provide CMR reference ranges in young, healthy individuals stratified by age, sex, general activity level, and weekly training hours. CONCLUSIONS: This work underscores the influence of age, sex, physical activity level, and type of sports on cardiac adaptation. We provide prediction interval-based CMR reference ranges of volumes, mass, ejection fraction, and strain to improve disease discrimination in athletes.