Aerobic capacity predicts skeletal but not cardiac muscle damage after a full distance Ironman triathlon - the Iron(wo)man-study

Purpose: This study examines the association between aerobic capacity and biomarkers of skeletal- and cardiac muscle damage among amateur triathletes after a full distance Ironman Methods: Men and women (N=55) were recruited from local sport clubs. One month before an Ironman triathlon, they conducted a 20m shuttle run test to determine aerobic capacity. Blood samples were taken immediately after finishing the triathlon, and analyzed for biomarkers of cardiac- and skeletal muscle damage. Regression models examining the association between aerobic capacity expressed in both relative terms (mLO2*kg-1*min-1) and absolute terms (LO2*min-1) controlled for weight and were fitted. Result: A total of 39 subjects (26% females) had complete data and were included in the analysis. No association between aerobic capacity and cardiac muscle damage but a significant negative association between aerobic capacity and skeletal muscle damage was observed. This association was independent of how aerobic capacity was expressed, although the model with aerobic capacity expressed in absolute terms and controlled for weight resulted in slightly higher r2 values, than when aerobic capacity was expressed in relative terms. Conclusion: A negative association between aerobic capacity and skeletal muscle damage was seen but despite the well-known cardio-protective health effect of high aerobic fitness no such association could be observed in this study.