Other Verifications of Decomposition Accuracy
Validation using mathematically synthesized signals
This approach uses a signal synthesized from artificially generated MUAPs and firing instances that are designated as the “truth”. The synthesized signal is decomposed and the accuracy is evaluated by comparing the decomposed data with the truth data.
But, the use of a mathematically synthesized signal is a generic test used under artificial circumstances. It requires the presumption that the accuracy results obtained under artificial conditions provide a faithful representation of the decomposition accuracy of a real sEMG signal. This is a difficult point to establish when the mathematically synthesized signal does not contain some of the complexities found in real physiological signals. For example current mathematical models use fabricated MUAPs that are unrealistically smooth because they are generated by models where the depolarization is surrounded by a homogeneous environment as is evidenced by the volume conductor model proposed by Merletti et al (1999), Farina and Merletti (2001) and Lowery et al (2002). The artificial smooth shapes of the MUAPs do not capture and represent the richer irregular details of the shapes of real MUAPs nor do they consider the changes in MUAP shape that occur in normal physiological conditions. In addition, currentmathematical models use fabricated motor unit firing instances that are either constructed artificially, as was done by Holobar and Zazula (2007) and Holobar et al (2012), or are derived from a generic model, such as that reported by Fuglevand et al (1993). These approaches fail to integrate known and documented physiological firing behavior such as synchronization and common drive. Yet, they have been used extensively by Holobar and Zazula (2004), Holobar et al (2009) and Holobar et al (2014) as the primary validation of the CKC decomposition algorithm. Because mathematically synthesized models do not directly assess the decomposition of a real sEMG signal the accuracy of individual extracted MUAPTs cannot be measured and remains unknown.