Differences in postural sway among healthy adults are associated with the ability to perform steady contractions with leg muscles

Davis, Leah A.; Allen, Stephen; Hamilton, Landon D.; Grabowski, Alena M.; Enoka, Roger M.

doi:10.1007/s00221-019-05719-4

Cited by 35 publications

(52 citation statements)

References 57 publications

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“…Although we demonstrate no functional improvements in the displacement of centre of pressure during unilateral balance tasks post-training, FORCE CoV has previously been correlated with balance measures (Kouzaki & Shinohara, 2010; Oshita & Yano, 2010; Davis et al, 2020b). For example, FORCE CoV assessed via low intensity isometric contractions in the plantar flexors was significantly associated with balance performance with eyes closed (determined by the time, in seconds, to complete the test) in both young and older individuals.…”

Section: Discussioncontrasting

confidence: 79%

“…However, one study demonstrated this association for contractions at 20%, but not 10% MVC (Oshita & Yano, 2010), and another for contraction intensities ≤5% MVC (determined via displacement of centre of pressure) (Kouzaki & Shinohara, 2010). Davis and colleagues also demonstrate FORCE CoV of the hip abductors and dorsiflexors to be the most significant explanatory variable during light load contractions to explain variance in sway-area rate across most balance conditions, although most of the variance across conditions was unexplained; suggesting other physiological mechanisms important for postural control likely influence unilateral balance (Davis et al, 2020b). The effects of force accuracy training on functional outcomes such as unilateral balance remains, therefore, to be further examined in other muscle groups and populations such as older individuals, who display deterioration of unilateral balance with advancing age (Maki et al, 1990; Izquierdo et al, 1999; Hess & Woollacott, 2005).…”

Section: Discussionmentioning

confidence: 99%

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Training induced improvements in knee extensor force accuracy are associated with reduced vastus lateralis motor unit firing variability

Ely

Jones

Inns

et al. 2022

Preprint

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Background: Muscle force output during sustained submaximal isometric contractions fluctuates around an average value and is known to be influenced by variation in motor unit (MU) firing rates. MU firing rate variability seemingly reduces following exercise training interventions, however, much less is known with respect to peripheral MU properties. We therefore investigated whether targeted force accuracy training could lead to improved muscle functional capacity and control, in addition to determining any alterations of individual MU features. Methods: Ten healthy participants (7 females, 3 males, 27+/-6 years, 170+/-8 cm, 69+/-16kg) underwent a 4-week supervised, unilateral, force accuracy training intervention. The coefficient of variation for force (FORCECoV) and sinusoidal wave force tracking accuracy (FORCESinu) were determined at 25% maximal voluntary contraction (MVC) pre- and post-training. Intramuscular electromyography was utilised to record individual MU potentials from the vastus lateralis (VL) muscles at 25% MVC during sustained contractions, pre- and post-training. Results: Knee extensor muscle strength remained unchanged following training, with no improvements in unilateral leg-balance. FORCECoV and FORCESinu significantly improved in only the trained knee extensors by ~13% (p=0.01) and ~30% (p<0.0001) respectively. MU firing rate variability significantly reduced in the trained VL by ~16% (n=8; p=0.001), with no further alterations to MU firing rate or neuromuscular junction transmission instability. Conclusion: Our results suggest muscle force control and tracking accuracy is a trainable characteristic in the knee extensors, which is likely explained by the reduction in MU firing rate variability apparent in the trained limb only.

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Section: Discussioncontrasting

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Training induced improvements in knee extensor force accuracy are associated with reduced vastus lateralis motor unit firing variability

Ely

Jones

Inns

et al. 2022

Preprint

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“…The mechanistic basis of the age-related loss of force control is multifactorial and has been speculated to relate to alterations in the neural input to MUs and consequent changes in their discharge properties (Castronovo et al, 2018 ) and to a loss of MUs and consequent MU remodeling (Challis, 2006 ). Recent evidence has suggested that this age-related loss of force control contributes to a reduced ability to perform activities of daily living (ADLs; Feeney et al, 2018 ; Davis et al, 2020 ).…”

Section: Introductionmentioning

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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“…For example, no study to date has sought to determine how much variance in the performance of functional tasks force complexity accounts for. This is in contrast to the magnitude of force variability, which has been demonstrated to account for significant variance in the performance of manual dexterity (Feeney et al., 2018) and balance tasks (Davis et al., 2020). Importantly, the adaptive significance of complexity has been demonstrated for other physiological outputs, which suggests that it will also have significance for the neuromuscular system.…”

Section: Evidence Of Complexity In Neuromuscular Outputmentioning

confidence: 89%

Physiological complexity: influence of ageing, disease and neuromuscular fatigue on muscle force and torque fluctuations

Pethick

Winter

2021

Experimental Physiology

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New Findings What is the topic of this review?Physiological complexity in muscle force and torque fluctuations, specifically the quantification of complexity, how neuromuscular complexityis altered by perturbations and the potential mechanism underlying changes in neuromuscular complexity. What advances does it highlight?The necessity to calculate both magnitude‐ and complexity‐based measures for the thorough evaluation of force/torque fluctuations. Also the need for further research on neuromuscular complexity, particularly how it relates to the performance of functional activities (e.g. manual dexterity, balance, locomotion). Abstract Physiological time series produce inherently complex fluctuations. In the last 30 years, methods have been developed to characterise these fluctuations, and have revealed that they contain information about the function of the system producing them. Two broad classes of metrics are used: (1) those which quantify the regularity of the signal (e.g. entropy metrics); and (2) those which quantify the fractal properties of the signal (e.g. detrended fluctuation analysis). Using these techniques, it has been demonstrated that ageing results in a loss of complexity in the time series of a multitude of signals, including heart rate, respiration, gait and, crucially, muscle force or torque output. This suggests that as the body ages, physiological systems become less adaptable (i.e. the systems’ ability to respond rapidly to a changing external environment is diminished). More recently, it has been shown that neuromuscular fatigue causes a substantial loss of muscle torque complexity, a process that can be observed in a few minutes, rather than the decades it requires for the same system to degrade with ageing. The loss of torque complexity with neuromuscular fatigue appears to occur exclusively above the critical torque (at least for tasks lasting up to 30 min). The loss of torque complexity can be exacerbated with previous exercise of the same limb, and reduced by the administration of caffeine, suggesting both peripheral and central mechanisms contribute to this loss. The mechanisms underpinning the loss of complexity are not known but may be related to altered motor unit behaviour as the muscle fatigues.

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Differences in postural sway among healthy adults are associated with the ability to perform steady contractions with leg muscles

Cited by 35 publications

References 57 publications

Training induced improvements in knee extensor force accuracy are associated with reduced vastus lateralis motor unit firing variability

Training induced improvements in knee extensor force accuracy are associated with reduced vastus lateralis motor unit firing variability

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

Physiological complexity: influence of ageing, disease and neuromuscular fatigue on muscle force and torque fluctuations

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