BACKGROUND: Left atrial (LA) size and function are linked to exercise intolerance in heart failure, while associations between LA parameters and exercise performance remain unclear in athletes. OBJECTIVES: This study aimed to identify correlations between echocardiographic LA size, pressure, stiffness, and composite indices, and various exercise performance indicators. METHODS: Echocardiographic parameters were obtained from 181 physically active military personnel receiving regular training and tests for a 3-km run and 2 min of push-ups and sit-ups. The top 16% of runners were compared sex-specifically, with the remaining 84% as controls to identify LA discriminators for running capacity. LA composite indices were defined as the LA volume index (LAVI) divided by the stiffness index (LASI) or pressure index (mitral E/e'). Spearman correlations were used to identify LA correlates with exercise performance. Generalized linear regressions were used to identify LA predictors of exercise performance with adjustments for potential covariates. RESULTS: The top 16% of runners vs. controls had a lower LASI based on LA volume changes (LASI_v, 0.196 vs. 0.245, CONCLUSIONS: The LAVI-to-LASI_v ratio, comprising LA size and stiffness information, was the best correlate across exercise types, while the LAVI-to-mitral E/e' ratio, comprising LA size and pressure information, was the best correlate of an endurance exercise, i.e., 3-km running performance.