MUAPs were manually selected using signal trigger averaging with the patient exerting a weak to moderate effort so as to activate 2 to 5 MUAPs clearly seen on the baseline. Every effort was made to improve sharpness. The filters were set between 2 Hz to 10 kHz; the acquisition sensitivities were set at 100-500 μv/division and 5 ms/division. The duration of the MUAPs was determined manually after averaging at 100 μv/division and 5 ms/division. Polyphasic MUAPs, but not satellite potentials, were included in the analyses. MUAPs with

amplitude lower than 50μV and rise time longer than 500μsec were rejected. Twenty MUAPs were obtained from each muscle from 4-5 insertion points. The original stored data consisting of 20 averaged MUAPs from Inhibitors,research,lifescience,medical each muscle were re-analyzed Inhibitors,research,lifescience,medical for the purpose of this study using the mean duration and outlier methods and the results correlated with biopsy findings in the contralateral muscle. For the mean duration method, the duration of 20 MUAPs from each muscle were averaged

and the mean compared with normal values for age (3, 11). A muscle was categorized as neuropathic or myopathic if the mean MUAP duration was 20% above Inhibitors,research,lifescience,medical or below the mean normal values for age respectively. The 20 MUAPs were also analyzed by the outliers method (12). Outliers as defined by Stalberg are the upper or lower MUAP amplitude or duration values beyond which a normal Inhibitors,research,lifescience,medical individual has no more than 2 MUAPs. For the outliers method we used the upper and lower limit values of Oh (13). MUAPs less than 6μsecs in duration and /or less than 300μV in amplitude were defined as myopathic, while MUAPs longer than 17msec in duration and/or larger than 3,5mV in amplitude as neuropathic. Muscles with more than 2 MUAPs outside the limits

were considered check details abnormal. Muscle biopsies Open muscle biopsies were obtained from 20 vastus lateralis and 19 biceps brachii Inhibitors,research,lifescience,medical muscles. The biopsy was obtained from the contralateral muscle to that examined by QEMG. The selected muscle had a Medical research council (MRC) score more than 3. The pathologist reading the biopsies was not aware of the EMG result. Muscle biopsy findings were classified for the purpose of the study SB-3CT as myopathic; M1, increased variability in muscle fibre size involving both fibre types, M2, the presence of necrosis and/or regeneration, M3, the presence of endomysial fibrosis indicating chronicity and fibre loss and M4 alterations in the fibre architecture without significant fibre loss or variability in fibre size. Such abnormalities included ragged red and cytochrome c oxidase deficient fibres (Fig. 1). Biopsies were classified as neurogenic if there were angular atrophic fibres of both fibre types and/or the presence of type grouping, indicative of reinnervation (Fig. 1). Figure 1. Myopathic (M1, M2, M3, M4) and neuropathic (N1,N2) biopsy findings. For details see text. Asterix in M4 indicates a ragged red fibre.