Motor unit firing characteristics in patients with amyotrophic lateral sclerosis

In this study, we investigated the behavior of active motor units identified via analysis of electromyographic (EMG) signals recorded from the first dorsal interosseous (FDI) muscle using a quadrifilar needle electrode. Data was collected from control subjects and patients with both upper (UMN) and lower (LMN) motor neuron dominant forms of amyotrophic lateral sclerosis (ALS). EMG recordings were gathered during isometric contractions reaching 20 or 50 % of the force output produced during a maximum voluntary contraction (MVC). Recordings were processed using freely available EMG decomposition software (EMGLAB). Results showed differences in mean motor unit firing rates and variability between ALS patients and control subjects. Differences in mean motor unit firing rates and variability were also observed between ALS patients with LMN-and UMN-dominant forms of ALS.