This study sought to compare the cross-sectional associations between fitness and echocardiographic measures of cardiac structure and function.Cardiorespiratory fitness is inversely associated with heart failure risk. However, the mechanism through which fitness lowers heart failure risk is not fully understood.We included 1,678 men and 1,247 women from the Cooper Center Longitudinal Study who received an echocardiogram from 1999 to 2011. Fitness was estimated by Balke protocol (in metabolic equivalents) and also categorized into age-specific quartiles, with quartile 1 representing low fitness. Cross-sectional associations between fitness (in metabolic equivalents) and relative wall thickness, left ventricular end-diastolic diameter indexed to body surface area, left atrial volume indexed to body surface area, left ventricular systolic function, and E/e' ratio were determined using multivariable linear regression analysis.Higher levels of mid-life fitness (metabolic equivalents) were associated with larger indexed left atrial volume (men: beta = 0.769, p0.0001; women: beta = 0.879, p value ≤0.0001) and indexed left ventricular end-diastolic diameter (men: beta = 0.231, p0.001; women: beta = 0.264, p0.0001). Similarly, a higher level of fitness was associated with a smaller relative wall thickness (men: beta = -0.002, p = 0.04; women: beta = -0.005, p0.0001) and E/e' ratio (men: beta = -0.11, p = 0.003; women: beta = -0.13, p = 0.01). However, there was no association between low fitness and left ventricular systolic function (p = NS).Low fitness is associated with a higher prevalence of concentric remodeling and diastolic dysfunction, suggesting that exercise may lower heart failure risk through its effect on favorable cardiac remodeling and improved diastolic function.
