Lower apparent motor-unit discharge rates in simulated diabetic peripheral neuropathy reflect HD-sEMG-like selection...

Decomposition-based EMG studies have reported lower motor-unit (MU) discharge rates in diabetic peripheral neuropathy (DPN) than in controls at matched relative contraction intensities. Whether this reflects physiology or selective representation of active MUs remains unclear. We used a neuromuscular force-control model to simulate 50 paired subjects under a Normal and a simplified DPN-like condition. For each subject, the HD-sEMG-like estimate was the mean of 10 MUs drawn at random from those with discharge rates of 5-15 pps and an interspike-interval coefficient of variation ≤0.3; the known mean of all active MUs was the sole reference. At 20% MVC, the HD-sEMG-like estimate was lower in DPN (mean paired difference, DPN minus Normal: -0.48 pps; 95% BCa CI [-0.73, -0.25]; p < 0.001), whereas the complete active-MU population was higher in DPN (+1.03 pps; 95% BCa CI [0.93, 1.13]; p < 0.001), reflecting the lower twitch-to-tetanus ratio assigned to DPN MUs. The mean of all eligible MUs was also lower in DPN (-0.50 pps), so the reversal arose from eligibility, not from sample size. At 10% and 50% MVC, the HD-sEMG-like differences also remained negative (-0.27 and - 0.41 pps); the complete-population differences remained positive and varied with contraction intensity (p < 0.001). These simulations show that discharge-based MU eligibility criteria can reverse between-condition discharge-rate differences; therefore, lower rates in HD-sEMG-like samples do not necessarily indicate lower rates across the complete active-MU population.