Neuromuscular Function: High-Density Surface Electromyography

Martinez‐Valdes, Eduardo; Negro, Francesco

doi:10.1007/978-1-0716-3315-1_6

Cited by 2 publications

(1 citation statement)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The silhouette threshold for decomposition was set to 0.85. To improve decomposition accuracy, automatic decomposition results were augmented by iteratively re-estimating the spike train and correcting for missed spikes or substantial deviations in the discharge profile (Martinez-Valdes & Negro, 2023). The instantaneous motor unit firing rates were calculated as the inverse of the inter-spike intervals of the motor unit spike trains.…”

Section: Motor Unit Decompositionmentioning

confidence: 99%

Motor unit firing rate modulation is more impaired during flexion synergy-driven contractions of the biceps brachii in chronic stroke

Beauchamp,

Hassan,

McPherson

et al. 2023

Preprint

Self Cite

View full text Add to dashboard Cite

Following a hemiparetic stroke, individuals exhibit altered motor unit firing patterns during voluntary muscle contractions, including impairments in firing rate modulation and recruitment. These individuals also exhibit abnormal muscle coactivation through multi-joint synergies (e.g., flexion synergy). Here, we investigate whether motor unit firing activity during flexion synergy-driven contractions of the paretic biceps brachii differs from that of voluntary contractions and use these differences to predict changes in descending motor commands. To accomplish this, we characterized motor unit firing patterns of the biceps brachii in individuals with chronic hemiparetic stroke during voluntary isometric elbow flexion contractions in the paretic and non-paretic limbs, as well as during contractions driven by voluntary effort and by flexion synergy expression in the paretic limb. We observed significant reductions in motor unit firing rate modulation from the non-paretic to paretic limb (non-paretic – paretic: 0.14 pps/%MVT, 95% CI: [0.09 0.19]) that were further reduced during synergy-driven contractions (voluntary paretic – synergy driven: 0.19 pps/%MVT, 95% CI: [0.14 0.25]). Moreover, using recently developed metrics, we evaluated how a stroke-induced reliance on indirect motor pathways alters the inputs that motor units receive and revealed progressive increases in neuromodulatory and inhibitory drive to the motor pool in the paretic limb, with the changes greatest during synergy-driven contractions. These findings suggest that an interplay between heightened neuromodulatory drive and alterations in inhibitory command structure may account for the observed motor unit impairments, further illuminating underlying neural mechanisms involved in the flexion synergy and its impact on motor unit firing patterns post-stroke.

show abstract

Section: Motor Unit Decompositionmentioning

confidence: 99%

Motor unit firing rate modulation is more impaired during flexion synergy-driven contractions of the biceps brachii in chronic stroke

Beauchamp,

Hassan,

McPherson

et al. 2023

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

Intrinsic properties of spinal motoneurons degrade ankle torque control in humans

Beauchamp,

Pearcey,

Khurram

et al. 2023

Preprint

View full text Add to dashboard Cite

Motoneurons are the final common pathway for all motor commands and possess intrinsic electrical properties that must be tuned to control muscle across the full range of motor behaviors. Neuromodulatory input from the brainstem is likely essential for adapting motoneuron properties to match this diversity of motor tasks. A primary mechanism of this adaptation, control of dendritic persistent inward currents (PICs) in motoneurons by brainstem monoaminergic systems, generates both amplification and prolongation of synaptic inputs. While essential, there is an inherent tension between this amplification and prolongation. Although amplification by PICs allows for quick recruitment and acceleration of motoneuron discharge during discrete motor tasks, PICs must be deactivated to de-recruit motoneurons upon movement cessation. In contrast, during stabilizing or postural tasks, PIC-induced prolongation of synaptic inputs is likely critical for sustained motoneuron discharge. Here, we designed two motor tasks that show PIC amplification and prolongation may conflict and generate errors that degrade the precision of motor output in humans. This included a paradigm comprised of a discrete motor task superimposed atop a stabilizing task and a paradigm with muscle length-induced changes to the balance of excitatory and inhibitory inputs available for controlling PICs. We show that prolongation from PICs introduces deficits in ankle torque control and that these deficits are further degraded at shorter muscle lengths when PIC prolongation is greatest. These results highlight the necessity for inhibitory control of PICs and showcase issues that are introduced when inhibitory control is perturbed or constrained. Our findings suggest that, like sensory systems, errors are inherent in motor systems. These errors are not due to problems in the perception of movement-related sensory input but are embedded in the final stage of motor output.

show abstract

Neuromuscular Function: High-Density Surface Electromyography

Cited by 2 publications

References 47 publications

Motor unit firing rate modulation is more impaired during flexion synergy-driven contractions of the biceps brachii in chronic stroke

Motor unit firing rate modulation is more impaired during flexion synergy-driven contractions of the biceps brachii in chronic stroke

Intrinsic properties of spinal motoneurons degrade ankle torque control in humans

Contact Info

Product

Resources

About