Model-Based Analysis of Muscle Strength and EMG-Force Relation with respect to Different Patterns of Motor Unit Loss

Abstract

This study presents a model-based sensitivity analysis of the strength of voluntary muscle contraction with respect to different patterns of motor unit loss. A motor unit pool model was implemented including simulation of a motor neuron pool, muscle force, and surface electromyogram (EMG) signals. Three different patterns of motor unit loss were simulated, including (1) motor unit loss restricted to the largest ones, (2) motor unit loss restricted to the smallest ones, and (3) motor unit loss without size restriction. The model outputs including muscle force amplitude, variability, and the resultant EMG-force relation were quantified under two different motor neuron firing strategies. It was found that motor unit loss restricted to the largest ones had the most dominant impact on muscle strength and significantly changed the EMG-force relation, while loss restricted to the smallest motor units had a pronounced effect on force variability. These findings provide valuable insight toward our understanding of the neurophysiological mechanisms underlying experimental observations of muscle strength, force control, and EMG-force relation in both normal and pathological conditions.

Spatial Dependence of Log-Transformed Electromyography–Force Relation: Model-Based Sensitivity Analysis and Experimental Study of Biceps Brachii

“…Different motor unit recruitment ranges (40% and 80%of maximum excitation) and firing strategies (“onion skin” and reverse “onion skin”) were used in the motor neuron pool model. Although variation in these factors influenced the simulated EMG–force relation, as demonstrated in previous simulation studies [ 12 , 13 , 14 , 15 ], our data confirmed a similar trend of the slope changes of the log-transformed EMG–force relation with respect to different motor unit depth distributions (using the simulated two motor unit recruitment ranges and two firing strategies). For the sake of simplicity, the results from only one motor unit recruitment range (40% of maximum excitation) and firing strategy (reverse “onion skin”) are presented below.…”

“…This study examined the EMG–force relation with respect to the depth distributions of different motor units in a muscle. The relation between EMG amplitude and muscle force has been extensively studied by others [ 12 , 13 , 14 , 15 , 16 ]. Two typical forms of the EMG–force relation have been reported [ 28 ], namely an approximately linear relation and a curvilinear relation, in which EMG amplitude increases relatively faster than force.…”

“…Given that the same force signal was used for different channels, the spatial variation in EMG–force relation reflected mainly changes in EMG properties because of changes in the relative position between active motor units and the recording electrodes. While most previous simulation studies have investigated various motor unit factors that may impact the EMG–force relation [ 12 , 13 , 14 , 15 ], few have examined the effect of motor unit distribution within a muscle. Compared with the often-used random distribution of different motor units or muscle fiber types, Robertson and Johnston applied a weighting term to produce different fiber type content in deep and superficial muscle regions, resulting in a larger variety of EMG–force relations [ 16 ].…”

Neuromuscular Injury Method in Different Strength Sports Damage

“…Therefore, the injury mechanism of all forms of specialized training programs has not been studied and reported in previous studies. 4…”

Efeitos de neuropatias periféricas desmielinizantes em tarefas de controle motor estudados por meio de um modelo neuromuscular multiescala.

“…Esse aumento no CV da força ou torque após perda de MUs funcionais com axônios de menor diâmetro também foi observado em um modelo de pool de MUs apresentado em Huang et al (2021), em que foi simulada uma perda de 60% das MUs com axônios de menor diâmetro.…”