Ageing reduces persistent inward current contribution to motor neurone firing: Potential mechanisms and the role of exercise

Orssatto, Lucas B. R.; Blazevich, Anthony J.; Trajano, Gabriel S.

doi:10.1113/jp284603

Cited by 5 publications

References 66 publications

(130 reference statements)

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Common synaptic inputs and persistent inward currents of vastus lateralis motor units are reduced in older male adults

Guo,

Jones,

Škarabot

et al. 2024

GeroScience

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Although muscle atrophy may partially account for age-related strength decline, it is further influenced by alterations of neural input to muscle. Persistent inward currents (PIC) and the level of common synaptic inputs to motoneurons influence neuromuscular function. However, these have not yet been described in the aged human quadriceps. High-density surface electromyography (HDsEMG) signals were collected from the vastus lateralis of 15 young (mean ± SD, 23 ± 5 y) and 15 older (67 ± 9 y) men during submaximal sustained and 20-s ramped contractions. HDsEMG signals were decomposed to identify individual motor unit discharges, from which PIC amplitude and intramuscular coherence were estimated. Older participants produced significantly lower knee extensor torque (p < 0.001) and poorer force tracking ability (p < 0.001) than young. Older participants also had lower PIC amplitude (p = 0.001) and coherence estimates in the alpha frequency band (p < 0.001) during ramp contractions when compared to young. Persistent inward currents and common synaptic inputs are lower in the vastus lateralis of older males when compared to young. These data highlight altered neural input to the clinically and functionally important quadriceps, further underpinning age-related loss of function which may occur independently of the loss of muscle mass.

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Common synaptic inputs and persistent inward currents of vastus lateralis motor units are reduced in older male adults

Guo,

Jones,

Škarabot

et al. 2024

GeroScience

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

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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.

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Maximising neuromuscular performance in people with pain and injury: moving beyond reps and sets to understand the challenges and embrace the complexity

Murphy,

Rio,

Whife

et al. 2024

BMJ Open Sport Exerc Med

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Rehabilitative practice is often criticised for being non-individualised, monotonous and not well aligned with foundational principles that drive continued physiological adaptation(s). However, our understanding of neuromuscular physiology is rapidly increasing and the way we programme rehabilitation is improving. This viewpoint highlights some of the potential considerations around why the adaptations achieved during rehabilitation programmes may be suboptimal. We provide basic, clinician-focused discussion about potential confounding physiological factors, and put forward several exercise-based programming recommendations and novel approaches to consider in contemporary rehabilitative practice. Specifically, we outline several potential mechanisms contributing to poor muscle activation and function that might be present following musculoskeletal injury. However, clinicians require strategies capable of attenuating these impairments to restore proper function. Therefore, we also provide an overview of recommended strength and conditioning guidelines, and novel strategies (such as external pacing and electrical stimulation techniques) that clinicians can consider to potentially improve the efficacy of musculoskeletal rehabilitation.

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Ageing reduces persistent inward current contribution to motor neurone firing: Potential mechanisms and the role of exercise

Cited by 5 publications

References 66 publications

Common synaptic inputs and persistent inward currents of vastus lateralis motor units are reduced in older male adults

Common synaptic inputs and persistent inward currents of vastus lateralis motor units are reduced in older male adults

Intrinsic properties of spinal motoneurons degrade ankle torque control in humans

Maximising neuromuscular performance in people with pain and injury: moving beyond reps and sets to understand the challenges and embrace the complexity

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