Rewrite academically: The signal decomposition is rendered difficult by the fact that MUAPs belonging to different trains may occur at the same time, thus resulting in superposition of waveforms fin the EMG signal. Signal processing techniques can be used to resolve superimposed MUAP waveforms (Section 5.6.2).

Under ideal conditions, each MUAP waveform has a unique shape due to the unique geometrical distribution of the muscle fibers of the motor unit relative the electrode. Unfortunately, the design of a decomposition procedure cannot assume that MUAP shapes remain fixed throughout the recording, but various issues related to signal nonstationarity should be taken into account to attain robust performance. These issues are exemplified by significant changes in MDAP shape caused by small movements of the needle electrode and the gradual change in shape of a MUAP related to changes in contraction level. Several approaches to EMG signal decomposition have been presented where these issues are addressed to various extents; the interested reader is referred to the abundant literature available on this topic, see, e.g., [90–102]. The response should be in all capital letters.
user