Time-dependent left ventricular mechanical changes during prolonged moderate endurance exercise assessed by three-dimensional speckle-tracking echocardiography

Background While exercise-induced cardiac fatigue has been described following prolonged exercise, real-time assessment of left ventricular mechanics during exercise using three-dimensional echocardiography remains limited. Most previous studies have focused on pre- and post-exercise comparisons, leaving the temporal progression of mechanical adaptation during sustained exercise insufficiently characterized. Purpose To investigate time-dependent left ventricular functional changes during prolonged moderate-intensity exercise using three-dimensional speckle-tracking echocardiography. Methods Fifteen healthy adults (32±6 years, 13 men, VO2max 42.5±7.9 mL/kg/min) completed 180-minute semi-recumbent cycling at 60–70% VO2max under controlled laboratory conditions. Three-dimensional speckle-tracking echocardiography was performed at baseline, serially during exercise (5–180 minutes), and at recovery. Doppler-derived diastolic parameters were assessed concurrently. Time effects were analyzed using linear mixed models to characterize within-subject temporal adaptation. Results Heart rate increased progressively during exercise (124→135 bpm, p<0.001), consistent with heart rate drift. LV end-diastolic volume decreased over time (135→124 mL, p=0.003), which may reflect altered loading conditions during prolonged exercise, while ejection fraction remained stable (65–68%, p=0.822). Diastolic function progressively deteriorated, with a reduction in E/A ratio (1.13→0.87) and prolongation of IVRTc (102→130 ms; both p<0.001), without change in E/e′. Global longitudinal and circumferential strain were unchanged (p=0.392 and 0.939). LV twist increased early but declined significantly over time (p<0.001), despite preserved ejection fraction and strain. High-sensitivity troponin T did not increase. Although minor time-dependent variations were observed in glucose and lactate, values remained within physiological ranges. Conclusion Prolonged moderate endurance exercise is associated with time-dependent alterations in rotational mechanics and diastolic function under controlled conditions characterized by LV twist and IVRTc, without elevations in high-sensitivity troponin T. IVRTc remained prolonged during early recovery, suggesting that the impaired diastolic function does not recover immediately after the prolonged exercise. Moreover, the dissociation between preserved global systolic indices and declining LV twist suggests that twist may serve as a sensitive marker of subclinical cardiac fatigue during sustained exercise and may provide incremental information beyond conventional systolic measures.