This study investigates the influence of varying clamping forces on the electrochemical performance and current density distribution in proton exchange membrane (PEM) water electrolysis cells. Using segmented current measurement boards integrated in a flexible high-pressure test bench, the operando effects of clamping pressure on contact resistance and current distribution were characterized. The results show that moderate clamping forces improve homogeneity and reduce ohmic losses, while excessive pressure leads to performance degradation due to mechanical deformation and membrane dehydration. The findings provide valuable insights for the mechanical optimization of PEM electrolyzers to enhance efficiency and durability in practical applications.