Influence of central and peripheral motor unit properties on isometric muscle force entropy: A computer simulation study

Dideriksen, Jakob Lund; Elias, Leonardo Abdala; Zambalde, Ellen Pereira; Germer, Carina Marconi; Molinari, Ricardo Gonçalves; Negro, Francesco

doi:10.1016/j.jbiomech.2021.110866

Cited by 9 publications

(9 citation statements)

References 45 publications

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“…Magnitude- and complexity-based measures therefore quantify different aspects of force output and have different functional significance. The ApEn of muscle force output has been suggested to be affected by several confounding variables relating to the contractile properties of motor units, though these effects could be limited by analyzing the ApEn of motor unit discharge rates instead of force output (Dideriksen et al, 2021 ). Nevertheless, it has been recommended that both magnitude- and complexity-based measures should be used when characterizing force control (Goldberger et al, 2002 ; Pethick et al, 2021 ).…”

Section: State Of the Art And Recent Developmentsmentioning

confidence: 99%

Alterations in Muscle Force Control With Aging: Is There a Modulatory Effect of Lifelong Physical Activity?

Pethick

Piasecki

2022

Front. Sports Act. Living

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Recent technological developments have enabled significant advances in our understanding of the ability to voluntarily control muscle force output. The fluctuations inherent to muscle force output can be quantified according to both their magnitude and temporal structure (or “complexity”), with such quantification facilitating comparison of force control between distinct populations. In comparison to young adults, older adults exhibit an increase in the magnitude (i.e., decreased steadiness) and a decrease in the complexity (i.e., decreased adaptability) of force fluctuations, both of which are indicative of a loss of force control. There remain, however, key gaps in knowledge that limit our interpretation of this age-related loss of force control. One such gap relates to the effect of lifelong physical activity on force control. To date, research on aging and force control has largely been conducted on inactive or moderately active older adults. However, high levels of lifelong physical activity, such as that exhibited by Masters athletes, have been shown to have protective effects on the function and morphology of the neuromuscular system. Some of these effects (e.g., on impaired inhibitory transmission in the motor cortex and on motor unit discharge rates) have the potential to attenuate the age-related loss of force control, while others (e.g., greater motor unit remodeling capacity) have the potential to worsen it. We therefore propose that, in order to progress our knowledge of the effects of aging on force control, future studies must consider the potential modulatory effect of lifelong physical activity.

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Section: State Of the Art And Recent Developmentsmentioning

confidence: 99%

Alterations in Muscle Force Control With Aging: Is There a Modulatory Effect of Lifelong Physical Activity?

Pethick

Piasecki

2022

Front. Sports Act. Living

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“…To provide further insight into differences in muscle force CV between lifelong physically active and inactive older adults, future research must simultaneously measure muscle force output and motor unit spike trains (using high-density EMG) in these distinct populations. From such high-density EMG measurements, it would also be possible to derive the ApEn of the cumulative motor unit spike train, which has been speculated to be of greater utility than the ApEn of muscle force (Dideriksen et al ., 2022).…”

Section: Discussionmentioning

confidence: 99%

The effect of lifelong physical (in)activity on knee extensor force control

Pethick

2023

Preprint

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It is well-documented that older adults exhibit a greater magnitude and decreased complexity of muscle force fluctuations in comparison to young adults. To date, however, research on this age-related loss of force control has focused on heterogeneous groups of inactive/moderately active older adults, despite accumulating evidence that high levels of lifelong physical activity (such as that exhibited by Masters athletes) has a protective effect on neuromuscular function and morphology. The present study compared healthy young adults (aged < 35; n = 14), healthy but inactive older adults (aged > 55; n = 13) and Masters athletes (aged > 55; n = 14) in order to discern the effects of lifelong physical (in)activity on muscle force control. Force control was assessed during isometric knee extension contractions at 10, 20 and 40% maximal voluntary contraction (MVC) and was quantified according to the magnitude (coefficient of variation [CV]) and complexity (approximate entropy [ApEn]; detrended fluctuation analysis [DFA] α) of force fluctuations. Inactive older adults exhibited significantly greater CV, indicative of poorer force steadiness, than young adults and Masters athletes during contractions at 10, 20 and 40% MVC (allP< 0.001). There were no significant differences in CV between the young adults and Masters athletes. These results indicate that lifelong physical activity has a protective effect against the age-related loss of muscle force control and suggest that, up to this point, our understanding of the age-related loss of muscle force control has been confounded by the effects of physical inactivity.Key pointsAgeing is associated with a decrease in muscle force control (i.e., poorer steadiness and adaptability), though to date this has largely been studied in inactive older adultsLifelong physical activity, such as that exhibited by Masters athletes, has a protective role against many age-related decrements in neuromuscular physiology and functionThis study compared force control, during contractions at intensities typical of the requirements of activities of daily living, in healthy young adults, healthy but inactive older adults and age-matched Masters athletesMasters athletes exhibited significantly better force steadiness than their inactive counterparts and no difference in steadiness compared to young adultsLifelong physical activity appears to modulate the age-related loss of force control, indicating that our current understanding of this loss of force control may be contaminated by the negative effects of inactivity

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“…To further investigate how the contractile properties of motor units influence the transmission of alpha band oscillations into force output, we used a well-established model that simulates the sequence of events from the excitation of an ensemble of motor neurons to the generation of isometric force output. This model, initially proposed by Fuglevand et al (1993), has since been utilized in various studies (Taylor et al, 2002, Dideriksen et al, 2012, Dideriksen and Negro, 2018, Dideriksen et al, 2022, Gogeascoechea et al, 2023). The motor neuron parameters were selected based on an exponential distribution across the pool of motor neurons (Fuglevand et al, 1993).…”

Section: Methodsmentioning

confidence: 99%

“…The model with greater contraction time values (model 2) was used to simulate the muscle lengthening condition. Each model was repeated 10 times, as has been done in previous simulation studies (Dideriksen and Negro, 2018, Dideriksen et al, 2022). For each time, we computed the average z-coherence of motor units within delta (1-5 Hz), alpha (5-15 Hz) and beta (15-35 Hz) bands, following the same approach used on the experimental data.…”

Section: Methodsmentioning

confidence: 99%

Muscle contractile properties directly influence shared synaptic inputs to spinal motor neurons

Cabral,

Inglis,

Cudicio

et al. 2023

Preprint

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Alpha band oscillations in shared synaptic inputs to the alpha motor neuron pool can be considered an involuntary source of noise that hinders precise voluntary force production. This study investigated the impact of altering muscle length on the shared synaptic oscillations to spinal motor neurons, particularly in the physiological tremor band. Fourteen healthy individuals performed low-level dorsiflexion contractions at ankle joint angles of 90° and 130°, while high-density surface electromyography (HD-sEMG) was recorded from the tibialis anterior (TA). We decomposed the HDsEMG into motor units spike trains and calculated the motor units’ coherence within the delta (1-5 Hz), alpha (5-15 Hz) and beta (15-35 Hz) bands. Additionally, torque steadiness and torque spectral power within the tremor band was quantified. Results showed no significant differences in torque steadiness between 90° and 130°. In contrast, alpha band oscillations in both synaptic inputs and force output decreased as the length of the TA was moved from shorter (90°) to longer (130°), with no changes in delta and beta bands. In a second set of experiments, evoked twitches were recorded with the ankle joint at 70° and 130°, revealing longer twitch durations in the longer muscle lengthen condition compared to the shorter. These experimental results, supported by a simple computational simulation, suggest that increasing muscle length enhances the muscle’s low-pass filtering properties, influencing the oscillations generated by the Ia afferent feedback loop. Therefore, this study provides valuable insights into the interplay between muscle biomechanics and neural oscillations.

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Influence of central and peripheral motor unit properties on isometric muscle force entropy: A computer simulation study

Cited by 9 publications

References 45 publications

Alterations in Muscle Force Control With Aging: Is There a Modulatory Effect of Lifelong Physical Activity?

Alterations in Muscle Force Control With Aging: Is There a Modulatory Effect of Lifelong Physical Activity?

The effect of lifelong physical (in)activity on knee extensor force control

Muscle contractile properties directly influence shared synaptic inputs to spinal motor neurons

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