Quantification of jiggle in real electromyographic signals

Two parameters have been defined for quantifying jiggle: normalized consecu tive amplitude differences (CAD) and the cross-correlational coefficient of consecutive discharges (CCC). In real recordings, artifacts from several s ources may increase the variability of these parameters as they were origin ally defined. Two methodological modifications designed to overcome such a limitation are proposed: estimation of baseline fluctuation from segments o f the recording free from nearby concurrent motor unit potentials (MUPs), a nd waveform alignment of consecutive discharges by correlation maximization (CM), The results obtained by the original and modified methods were compa red for MUPs from normal subjects and patients with amyotrophic lateral scl erosis and chronic neurogenic diseases. With the modified method, CAD and C CC showed fewer extreme values and less scatter. The number of successfully aligned MUPs with the CM method was 18.8% higher (n = 394; Chi-square = 54 .6; P < 0.001), including irregular and unstable MUPs. The proposed modific ations improve our capability to quantify the jiggle of real signals and re duce the necessity of manual interventions although low-interference record ings and operator supervision are still required. (C) 2000 John Wiley & Son s, Inc.