Cardiovascular adaptation to training load in endurance athletes: a longitudinal study

Prior studies on cardiac remodelling associated with exercise have relied on self-reported data of uncertain accuracy. In the present study, exercise duration and intensity were objectively quantified using heart rate (HR) monitors in athletes, and these metrics were correlated with cardiac magnetic resonance findings.

Young (16-23 years, n = 69) and middle-aged (45-70 years, n = 82) male endurance athletes with ≥80% of training sessions recorded via chest-worn HR monitors over 3 months were included. Training duration, session count, and intensity (classified into five HR zones and expressed as Edwards training impulse in arbitrary units) were analysed. Cardiac magnetic resonance measured indexed left/right ventricular volumes, ejection fraction, and left ventricular mass.

Younger athletes trained more than older athletes [169 (127-209) vs 78 (49-114) hours; 23 129 (17 880-28 305) vs 12 620 (7168-17 607) arbitrary units; both P < .05] over a 3-month period. In all athletes, light-to-moderate-intensity training exceeded thresholds of >6 or >9 metabolic equivalent of tasks to describe intense activity. Training duration (r > .33, P < .05 for all) and Edwards training impulse (r > .29, P < .05 for all) correlated with cardiac dimensions, but the duration always outperformed intensity. Time spent in lower HR zones (1 and 2) correlated more with cardiac dimensions than higher-intensity training. Partial least squares analysis identified training duration in Zones 1&2 and 3 and age as key determinants of cardiac remodelling, whereas intensity was not a significant determinant of cardiac dimensions.

Objective exercise quantification reveals new insights into cardiac remodelling, highlighting total exercise duration as a primary determinant of left/right ventricular volumes, independent of intensity. Traditional questionnaire-based methods may overlook these relationships.