Impact of exercise intensity on cardiac function in adolescent runners

Background. Prolonged exercise may induce a transient reduction in the left ventricular (LV) function (exercise-induced cardiac fatigue) in adults. However, data related to the cardiovascular consequences of prolonged exercise in adolescents are extremely limited. This study examined the impact of exercise intensity adopted in routine long-distance run training on LV function in trained adolescent runners in a laboratory-based setting. Methods. Twelve male adolescent runners (14.5±1.5 years) performed two 90-min treadmill runs with intensity set at the running speeds that corresponded to either 80% (Tl) or 100% (T2) ventilatory threshold. LV function was examined echocardiographically pre- and post-exercise. Results. The two-factor repeated-measures ANOVA revealed no significant (P>0.05) main effects for the intensity and the interaction of intensityÍ pre- and postexercise in ejection fraction (EF), systolic blood pressure/end systolic volume ratio (SBP/ESV) and early to atrial diastolic flow velocity ratio (E:A). Nevertheless, the main effect for time course in EF was significant (P<0.05). Preexercise EF in T1 (74±5 vs• 70±5%, P<0.05), but not in T2 (75±4 vs. 72±7%, P>0.05), decreased significantly post-exercise, yet this did not reach clinical levels. Further, no difference (P>0.05) was found between pre- and post-exercise in SBP/ESV (T1: 3.9±0.9 vs. 3.7±1.1; T2: 4.0±0.7 vs. 4.6±1.9 mmHg•ml^-1) and E:A (T1: 1.87±0.11 vs. 1.87±0.11; T2:1.83±0.11 vs. 1.87±0.09) in both trials. Conclusion. These findings suggest that the training intensities adopted in routine long-distance run training in the adolescent runners do not seem to induce cardiac fatigue. Adolescent hearts appear to cope well with prolonged run performed on training.