Purpose: This study examined the effect of two bouts of prolonged exercise performed on the same day on cardiac biomarkers and left ventricular (LV) function in trained adolescent runners.
Methods: Twelve male adolescent runners (age = 14.5 ± 1.5 yr) performed two 45-min constant-load treadmill runs (RUN1 and RUN2), separated by 255 min of recovery, with intensity set at the running speeds that corresponded to ventilatory threshold. Serum cardiac troponin T (cTnT) and N-terminal pro-brain natriuretic peptide (NT-pro-BNP) were assessed before (PRE1, PRE2), immediately after (POST1, POST2), and 255 min after each run (POST1+4, POST2+4) where PRE2 and POST1+4 were the same sample. LV function was examined echocardiographically before and after each run.
Results: cTnT was undetectable at PRE1 and POST1 but was elevated in eight-twelfths (67%) of runners at POST1+4/PRE2 (median (range) = 0.018 (<0.01-0.375 ng·mL(-1))). cTnT decreased progressively thereafter up to POST2+4 (four-twelfths, 33%). Data for NT-pro-BNP were significantly increased at POST1 and POST2 but returned to baseline at POST1+4 and POST2+4. Ejection fraction (EF) was significantly reduced after RUN1 (74% ± 5% to 70% ± 5%, P < 0.05), although still within normal range. There was no evidence of a cumulative drop in EF after RUN2 because the change was similar in magnitude (73% ± 4% to 68% ± 5%, P < 0.05). The decrease in the early-atrial (E:A) diastolic flow velocity ratio was greater after RUN1 (1.91 ± 0.13 to 1.83 ± 0.08, P < 0.05) than after RUN2 (1.86 ± 0.15 to 1.85 ± 0.12, P > 0.05), and thus, changes were not cumulative.
Conclusions: Neither cardiac biomarkers (cTnT or NT-pro-BNP) nor LV function (EF or E:A) demonstrate cumulative changes after two 45-min runs at ventilatory threshold separated by ∼ 4 h of recovery. Adolescent hearts seem to cope well with two prolonged runs performed on the same day.