<p>Human in vivo determination of the moment-angle-angular velocity and muscle force-length-velocity relationships is typically based on dynamometry. Although inertial moment and axis misalignment are inevitable during active joint rotations, their effect on measurement errors during dynamic plantarflexions is unknown. We studied the effect of moment corrections during concentric plantarflexions at five pre-set angular velocities ranging from 45^o/s to 270^o/s and at the maximal and two submaximal levels of soleus muscle activation in fourteen healthy young participants. Omitting moment corrections led to considerable errors in the maximum measured moment of up to 39.5% and 86.5% in maximal and submaximal plantarflexions, respectively. Measurement errors also affected the time instants and ankle joint angles at which moment maxima were identified. The contribution of inertial moment and axis misalignment corrections to the occurring errors had a large inter-individual variability and depended both on angular velocity and muscle activation level. The contribution of inertial moment increased with angular velocity and muscle activation level, while the contribution of axis misalignment decreased with angular velocity and increased with muscle activation level. Therefore, we posit a strong necessity to account for these two often neglected corrections during dynamic plantarflexions.</p>