Strenuous physical exercise and hyperthermia may paradoxically induce oxidative stress and adverse effects on myocardial function. The purpose of this study was to investigate the effect of 14-d coenzyme Q 10 (CoQ ) supplementation and pre-cooling on serum creatine kinase-MB (CK-MB), cardiac Troponin I (cTnI), myoglobin (Mb), lactate dehydrogenase (LD), total antioxidant capacity (TAC), lipid peroxidation (LPO) and CoQ 10 10 concentration in elite swimmers. In total, thirty-six healthy males (mean age 17 (SD 1) years) were randomly selected and divided into four groups of supplementation, supplementation with pre-cooling, pre-cooling and control. During an eighteensession protocol in the morning and evening, subjects attended speed and endurance swimming training sessions for 5 km in each session. Blood sampling was done before (two stages) and after (two stages) administration of CoQ and pre-cooling. ANCOVA and repeated measurement tests with Bonferroni post hoc test were used for the statistical analysis of the data. There was no significant statistical difference among groups for the levels of CK-MB, cTnI, Mb, LD, TAC, LPO and CoQ 10 10 at the presampling (stages 1 and 2) (P >0·05). However, precooling and control groups show a significant increase in the levels of CK-MB, cTnI, Mb, LD and LPO compared with the supplementation and supplementation with pre-cooling groups in the post-sampling (stages 1 and 2) (P <0·05), except for the TAC and CoQ . Consequently, CoQ supplementation prevents adverse changes of myocardial damage and oxidative stress during swimming competition phase. Meanwhile, the pre-cooling strategy individually has no desired effect on the levels of CK-MB, cTnI, Mb, LD, LPO, TAC and CoQ 10 10 10 .
