Only a few studies have assessed the kinetics of cardiac troponins after endurance exercise by using the novel high-sensitive (HS) immunoassays. These were based on the measurement of HS-TroponinT (TnT), but not HS-Troponin I (TnI), and exclusively involved marathon or ultra-marathon contests. TnI was measured in 17 healthy trained Caucasian males performing a 21 km, half-marathon, with the conventional AccuTnI and the HS-AccuTnI immunoassays. The concentration of HS-AccuTnI significantly increased from the mean baseline value of 2.9 ng/L (Interquartile range [IQR], 2.4- 4.3 ng/L) to 4.8 (IQR, 3.0-5.7 ng/L) after the run (p = 0.002), 9.0 ng/L (IQR, 5.8-15.3 ng/L) at 3h (p < 0.001), 12.3 ng/L (IQR, 7.1-21.5 ng/L) at 6h (p < 0.001), and 4.5 ng/L (IQR, 2.8-6.0 ng/L) at 24 h (p = 0.003) afterwards. The variation throughout the study period was statistically significant (p < 0.001). Age, training history, finishing time and exercise intensity were not associated with changes of HS-AccuTnI. The values of the TnI measured with the conventional AccuTnI immunoassay were always below the 99th percentile reference limit, except in one subject 3 h after the run, and in two subjects 6 h after the run. These results attest that TnI values measured with the novel HS-AccuTnI immunoassay were significantly increased in athletes participating in a half marathon.