Motor unit number index: Guidelines for recording signals and their analysis

Abstract

Introduction: This study proposes guidelines for motor unit number index (MUNIX) recording and analysis.

Methods: MUNIX was measured in control participants and in patients with amyotrophic lateral sclerosis. Changes in MUNIX values due to E1 electrode position, number of surface electromyography interference pattern (SIP) epochs, SIP epoch duration, force of contraction, and outlier data points were investigated.

Results: MUNIX depends on optimized compound muscle action potential (CMAP) amplitude. Individual muscles showed variations when the number of epochs was low or when the SIP duration was short. Longer SIP duration allowed better recognition of artifacts. MUNIX results were affected by SIP values at all force levels but was more affected when SIP area was low.

Discussion: We recommend changing the E1 electrode position to maximize CMAP amplitude. Twenty or more SIP signals of 500-ms duration should be recorded by using force levels ranging from slight to maximum. Traces should be reviewed to identify and exclude signals with tremor or solitary spikes. Muscle Nerve 58: 374-380, 2018.

Keywords: MUNIX; artifacts; compound muscle action potential; guidelines; motor unit number index; surface EMG interference pattern; tremor.