Turn analysis of the EMG: the amplitude definition of a turn

Traditionally and arbitrarily an EMG interference signal (EMGIP) "turn" is defined as any 100 microV signal amplitude change. There have not been planned studies challenging this definition. Here, EMGIPs, recorded by coaxial needle electrodes, in MVC, from biceps brachii muscles of 143 subjects, in three diagnostic groups (Normals, Neuropathics, Myopathics), were analyzed in search of the effects of different turn definition amplitude values (TDEF) on the EMGIP number of turns, average turn amplitude, their ratio, and on the cumulative turn amplitude. This study shows significant differences between the diagnostic-groups. It shows that TDEF has significant effect on the number of turns, the average turn amplitude, their ratio, the cumulative amplitude, and that certain TDEFs are significantly better than others in the diagnosis of neuromuscular diseases. Also, it shows that the number of turns and the turns to average amplitude ratio are better measurements than the average turn amplitude and than the cumulative turn amplitude in showing differences between the EMGIPs of the various diagnostic-groups. As such, some of the smaller TDEFs are significantly better diagnostically than the traditional 100 microV value. Also, it shows that better discrimination between the diagnostic-groups may be achieved by applying more than one TDEF value onto the same data. This study leaves the question of the best TDEF or best TDEF sets open for further research in similar and in different paradigms and technical settings.