Background: It is well known that ultra-endurance races such as a full distance ironman triathlon causes damage to skeletal and cardiac muscles. However, the underlying factors causing these disturbances are less investigated. In this study we investigated if there is an association between ground reaction forces, measured with accelerometry, during the marathon part of an Ironman triathlon and markers of skeletal and cardiac muscle damage. Our hypothesis is that higher ground reaction forces is positively associated with skeletal and heart muscle damage with no difference between the genders in this association.

Methods: In all 20 (8 women) subjects completed a full distance ironman triathlon (3.8 km swimming, 180 km cycling and 42 km running) and provided a full set of data and was included in the analysis. As markers for skeletal muscle damage, creatin kinas (CK) and myoglobin was analysed. As markers for cardiac muscle damage cardiac troponin t (cTnT), the N-terminal of the prohormone brain natriuretic peptide (NT-proBNP) was analysed. Ground reaction forces was estimated using an accelerometer (ActiGraph GT3x). Based on the official transition times we sliced out the raw accelerations for the marathon part of the race and calculated the mean vector magnitude (VM) expressed in milliG per second (mG/s). Due to outliers among the dependent variables, Spearman rank correlations (rho) stratified by sex was calculated.

Results: As seen in figure 1, no significant association between the biomarkers and mechanical stress was observed (all p>0.05).

Conclusion: We did not find any support to our initial hypothesis that there should be a positive association between ground reaction forces and markers of skeletal and heart muscle damage. The small sample size in the groups and the fact that we did not adjust for any potential confounder in this study warrants causing in the interpretation of the results.