Nowadays high temperature polymer electrolyte fuel cells suffer from performance and long-term stability issues. Detailed understanding of the degradation effects is thus a key aspect for the improvement of this type of fuel cells. Degradation can be categorized into thermal, (electro-) chemical and mechanical effects. This paper focuses on the latter process, investigating two different types of membrane electrode assemblies by accelerated stress tests at high current densities in which, compared to common procedures, the device is driven at higher current densities between 0.6 – 1.0 A/cm². In addition to voltammetry and polarization curves, the assemblies are analyzed by electron microscopy methods and especially micro-computed tomography which allows a non-destructive investigation of the hidden interfaces within the MEA structure, giving a direct view on mechanical defects. Load cycling at high current densities revealed significant contributions to the degradation of the catalyst layer. But no influence on the membrane could be found.