Intra-individual variability of markers of skeletal and heart muscle damage after two full distance Ironman: the Iron(WO)man study

Abstract Purpose To examine the tracking, i.e., the stability, of response in biomarkers signaling cardiac- and skeletal muscle damage after two full distance Ironman races separated by one year. Methods Thirteen individuals (7 females) who participated in two Ironman races in Sweden year 2015 and 2016 and had been included in the Iron(WO)man study were investigated. Blood samples were drawn immediately after the race and were analyzed for cardiac troponin T, N-terminal of the prohormone brain natriuretic peptide, myoglobin, creatine kinase and serum creatinine. Stability of the biomarker response between the year-to-year was estimated by calculating tracking coefficients using Spearman correlation. Results There were no intra-individual differences in the post-race values in any of the studied biomarkers (all p > 0.05). All tracking coefficients showed a substantial stability (rho = 0.60–0.77). Conclusion It appears that there are individuals who are at particular risk of getting high levels of biomarkers signaling cardiac and skeletal muscle damage. However, this secondary analysis was neither designed nor powered to give definite answers and could not rule out the possibility that higher markers in fact represent occult heart disease.