Steadiness is reduced and motor unit discharge is more variable in old adults

Laidlaw, Douglass H.; Beznoska, Martin; Enoka, Roger M.

doi:10.1002/(sici)1097-4598(200004)23:4<600::aid-mus20>3.0.co;2-d

Cited by 341 publications

(165 citation statements)

References 37 publications

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“…Here, decreased accuracy was shown by higher NMAE and NPAE, and decreased steadiness was shown by increased NSAE (figure 2a) in force fluctuations with increased levels of force-matching tasks, at 15 per cent when compared with at 20 per cent MVICs. These results are in agreement with the previous studies which reported that higher levels of submaximal force output resulted in greater inaccuracy and unsteadiness, in particular at lower levels of effort (Enoka et al 1999;Slifkin & Newell 1999;Laidlaw et al 2000).…”

Section: Discussionsupporting

confidence: 93%

Effect of fatigue on force fluctuations in knee extensors in young adults

Singh

Arampatzis

Duda

et al. 2010

Phil. Trans. R. Soc. A.

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This study investigated the hypothesis that fatiguing exercises led to increased force fluctuations during submaximal isometric knee extensions and to decreased accuracy and steadiness in the time and frequency domains. Sixteen young adults (eight males, eight females) were tested, in a seated posture with 90°knee flexion, to assess their ability to reproduce target extensor torques set at 15 per cent and 20 per cent of their maximum voluntary isometric contraction, both before and after fatiguing exercises. Normalized mean (NMAE) and peak (NPAE) of the absolute error were both used to quantify accuracy, whereas normalized standard deviation of the absolute error (NSAE) was used to quantify steadiness of the torque trials in the time domain. Mean and median power frequencies (MnPF, MdPF) and normalized peak power (NPkP) were used to assess the spectral structure of the torque signals. NMAE, NSAE and NPAE all showed excellent intra-as well as intersession reliabilities (intraclass correlation values greater than 0.75 and low standard error of measurement values), demonstrating repeatability of the test set-up. NMAE, NSAE and NPAE increased significantly postfatigue (greater than 42%), together with a shift towards higher frequency (MnPF and MdPF) components, indicating that the set-up was sensitive enough to detect the decreased force accuracy and steadiness of the musculature after fatigue. Increased force variability in both the time and frequency domains could therefore explain decreased steadiness after fatigue.

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Section: Discussionsupporting

confidence: 93%

Effect of fatigue on force fluctuations in knee extensors in young adults

Singh

Arampatzis

Duda

et al. 2010

Phil. Trans. R. Soc. A.

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“…In general, the lesser EMG during an eccentric contraction when lowering a given load (6,42) is attributed to a lower discharge rate and the recruitment of fewer motor units (6,23,34). The reduction in discharge rate likely includes an increased variability in discharge (12,23,29,30), which can decrease twitch fusion and increase the fluctuations in the forces exerted by individual motor units (12,14). Some evidence indicates that discharge rate variability of the motor units and fluctuations in motor output increase with movement speed for both concentric (40,41) and eccentric contractions (22).…”

Section: Discussionmentioning

confidence: 99%

“…One prediction of this theory is that the accuracy of goaldirected movements should decline as the amplitude of the force fluctuations increases. Therefore, the accuracy of goal-directed movements should vary with changes in movement velocity (41), the type of muscle contraction performed (2, 3, 5), and the age of the individual (1,12,15,23,38).The purpose of the study was to assess the effect of movement velocity on the fluctuations in acceleration and the ability to achieve a target velocity when young and old adults performed anisometric contractions with the first dorsal interosseus muscle. The results were consistent with the prediction of the minimum variance theory that movement accuracy declines with an increase in the fluctuations of acceleration; nonetheless, the relations differed for young and old adults.…”

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confidence: 99%

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Fluctuations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults

Christou

Shinohara

Enoka

2003

Journal of Applied Physiology

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Christou, Evangelos A., Minoru Shinohara, and Roger M. Enoka. Fluctuations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults. J Appl Physiol 95: 373-384, 2003. First published March 21, 2003 10.1152/japplphysiol.00060. 2003.-The purpose of the study was to assess the effect of movement velocity on the relation between fluctuations in acceleration and the ability to achieve a target velocity during voluntary contractions performed by young (29.5 Ϯ 4.3 yr) and old (74.9 Ϯ 6.2 yr) adults. Subjects performed concentric and eccentric contractions with the first dorsal interosseus muscle while lifting a submaximal load (15% of maximum) at six movement velocities (0.03-1.16 rad/s). Fluctuations in acceleration, the accuracy of matching the target velocity, and electromyographic (EMG) activity were determined from three trials for each contraction type and movement velocity. The fluctuations in acceleration increased with movement velocity for both concentric and eccentric contractions, but they were greatest during fast eccentric contractions (ϳ135%) when there was stronger modulation of acceleration in the 5-to 10-Hz bandwidth. Nonetheless, EMG amplitude for first dorsal interosseus increased with movement velocity only for concentric and not eccentric contractions. Consistent with the minimum variance theory, movement accuracy was related to the fluctuations in acceleration for both types of contractions in all subjects. For a given level of fluctuations in acceleration, however, old subjects were three times less accurate than young subjects. Although the EMG amplitude at each speed was similar for young and old adults, only the young adults modulated the power in the EMG spectrum with speed. Thus the fluctuations in acceleration during voluntary contractions had a more pronounced effect on movement accuracy for old adults compared with young adults, probably due to factors that influenced the frequency-domain characteristics of the EMG. concentric contraction; eccentric contraction; electromyogram; first dorsal interosseus; frequency spectrum THE FORCE EXERTED BY A MUSCLE during a voluntary contraction is not constant, but rather it fluctuates about an average value (2,15,25,33,36). The neural mechanisms most responsible for the fluctuations in the force exerted by hand muscles appear to be the regularity with which motoneurons discharge action potentials and the common modulation of motor unit discharge in the agonist and antagonist muscles (7,10,13,16,41). Fluctuations in muscle force impose a significant constraint on the ability of the nervous system to control movement by influencing the capacity to exert a desired force and to achieve an intended trajectory (17,18,43).The minimum variance theory postulates that the central nervous system attenuates this constraint during the performance of goal-directed movements by selecting activation strategies that minimize the variance in the trajectory of the movement (18,43). One prediction of this theory is t...

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“…In addition, lengthening contractions are also associated with reduced motor performance [12][13][14]. Interestingly, the magnitude of this deficit is thought to be increased by advancing age, with greater impairments in performance observed in old adults during lengthening movements [13,[15][16][17][18], which may contribute to the increased incidence of falls in the elderly [19].…”

Section: Introductionmentioning

confidence: 99%

Intracortical Inhibition Assessed with Paired-Pulse Transcranial Magnetic Stimulation is Modulated during Shortening and Lengthening Contractions in Young and Old Adults

Opie

Semmler

2016

Brain Stimulation

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In all cases accepted manuscripts should: link to the formal publication via its DOI  bear a CC-BY-NC-ND license -this is easy to do, click here to find out how  if aggregated with other manuscripts, for example in a repository or other site, be shared in alignment with our hosting policy  not be added to or enhanced in any way to appear more like, or to substitute for, the published journal article Embargo 1935-861X Brain Stimulation 129 May 2017 Age-and movement-related changes in intracortical inhibitionPage 2 AbstractBackground: The modulation of intracortical inhibition is thought to be impaired in older

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Steadiness is reduced and motor unit discharge is more variable in old adults

Cited by 341 publications

References 37 publications

Effect of fatigue on force fluctuations in knee extensors in young adults

Effect of fatigue on force fluctuations in knee extensors in young adults

Fluctuations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults

Intracortical Inhibition Assessed with Paired-Pulse Transcranial Magnetic Stimulation is Modulated during Shortening and Lengthening Contractions in Young and Old Adults

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