Frequency analysis and duration of motor unit potentials: reliability and diagnostic usefulness

We studied the correlation, reliability and diagnostic usefulness of different time and frequency parameters of motor unit potentials (MUPs). Most frequency parameters were redundant because of high correlation with conventional MUP parameters. Variable selection algorithms for discriminant analysis indicated that center frequency (CENTFR) and spike duration (SPD) improved the discrimination between MUPs from normal, myopathic and neuropathic muscles. This was corroborated by univariate statistical tests comparing mean MUP duration (DUR), mean CENTFR and mean SPD of pathological muscles with those of normal muscles. One-sided tests for increased mean SPD improved the sensitivity for neurogenic changes and one-sided tests for reduced mean CENTFR improved the sensitivity for myopathic changes. The rate of false positive results did not increase by these additional tests. The retest reliability of CENTFR was superior to that of DUR. CENTFR and SPD are recommendable new parameters for quantitative MUP analysis based either on multi- or univariate statistics.