Neural Noise- Maximal motor unit firing rates decline with amyotrophic lateral sclerosis (ALS) progression.1
- Motor unit firing rates derived from EMG provide electrophysiological markers of disease progression in ALS.1 1
Weekly enrichment (2026-07-20)
- The study (Clinical Neurophysiology, 2026; Fernandes et al.) enrolled 93 people with ALS; after excluding single-visit participants (40) and those without decomposable motor units (14), 39 were analyzed (24 men, mean age 63 ± 16 years) across up to five visits ~20 ± 8 weeks apart, spanning roughly 18 months.2
- Recordings were from the tibialis anterior using a 64-channel HD-sEMG grid (8.0 mm inter-electrode distance), monopolar, band-pass filtered 10–500 Hz, sampled at 2000 Hz, and decomposed with a convolution-kernel-compensation algorithm (DEMUSE); only motor units with pulse-to-noise ratio ≥ 30 dB were kept, yielding 1,547 units.2
- Maximal motor unit firing rates declined significantly over time at −0.32 Hz per month (95% CI −0.44 to −0.19), independent of MRC strength scores.2
- Firing rate fell by 2.38 Hz (95% CI 1.78–2.98) for each 1-point drop in MRC and by 0.54 Hz (−0.83 to −0.26) for each ALSFRS-R point lost.2
- The decline appeared even in clinically strong, pre-symptomatic limbs (MRC = 5), suggesting firing-rate analysis can detect neuromotor deterioration before weakness is clinically measurable.2
- Conventional bipolar surface EMG RMS amplitude showed no significant change over time, so individual-motor-unit firing rates were more sensitive to progression than RMS amplitude or the MRC scale.2
- Baseline cohort characteristics: mean ALSFRS-R 34 ± 6.6 (of 48), symptomatic-limb MRC 3 ± 1.1, and 23 pre-symptomatic limbs tested.2
- For context, prior HD-sEMG work in ALS found abnormally high firing rates during submaximal contractions cross-sectionally; this study extends the picture to maximal contractions, which recruit high-threshold motor units that degenerate early in the disease.3