Increases in High-Sensitivity Cardiac Troponin I in Athletes during a Long-Term Period of Routine Training Out of Competition

Cardiac troponin I (cTnI) concentrations have been shown to increase in athletes after high-endurance exercise (1,). Different theories have been put forward to explain this phenomenon including cTnI release from the cytosol, increased myocyte membrane permeability, inflammation, and cardiac stress during exercise (1). However, data on variation of cTnI in athletes during stable training conditions are lacking. We aimed to assess whether cTnI concentrations increase during stable training conditions, and, if so, the duration of the increased concentrations, the influence of high-intensity exercise, and the time since the last training session. The study population consisted of 30 healthy athletes (15 males), aged 19–53, recruited from triathlon clubs. Inclusion criteria were: training more than 13 h per week, normal medical examination (no physical injury, cardiovascular, kidney, or other chronic disease) and normal routine laboratory test results, a normal stress test including electrocardiogram, and no hospitalization during the previous 4 weeks. High-endurance exercise was defined as training sessions with a heart rate (HR) >82% of the maximum HR. Eleven monthly samples were collected per athlete at 8–10 AM on weekdays under standardized preanalytical conditions (10 h fasting, no high-endurance exercise the previous 24 h and being out of competition the previous week). Subjects filled in a questionnaire at each visit including health status, medication, last competition, last training, and changes in diet. The study was approved by the Hospital Ethical Committee and written consent was obtained from all participants. Serum samples were stored at −80 °C with hs-cTnI measured in duplicate on an Atellica Solution system (Siemens Healthineers). All samples from each athlete were analyzed in the same analytical run. Internal quality control was performed at two levels (37 and 5486 ng/L; CVA 3.9 and 2.7%, respectively) and the assay LoD was 1.3 ng/L. The 99th percentiles were 39 and 54 ng/L for females and males, respectively. Statistical analyses included Mann–Whitney and Pearson tests to compare hs-cTnI values in samples taken following nonhigh-endurance exercise during the previous 24 h in samples collected after a rest period. The correlation between hs-cTnl and the elapsed time since the last exercise was also examined.