TNNI3 and acute coronary syndrome: In this regard, although serum levels of cTn (either cTn-I or c-Tn-T), a marker of injury in acute coronary syndrome, are frequently elevated 24 h post-marathon in amateur runners (38) this transient increase in cTn probably reflects the cytosolic release of the biomarker, which is due to altered cardiomyocyte metabolism (39), not true necrosis, as suggested by a study using delayed enhancement cardiac magnetic resonance imaging (40).