Discharge pattern of human motor units during dynamic concentric and eccentric contractions

Kossev, A; Christova, Peka

doi:10.1016/s0924-980x(98)00012-5

Cited by 83 publications

(88 citation statements)

References 38 publications

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“…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). Therefore, the greater relative increase in acceleration fluctuations during the eccentric contractions may be due to increased discharge rate variability of the involved motor units.…”

Section: Discussionmentioning

confidence: 99%

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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Section: Discussionmentioning

confidence: 99%

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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“…Both force release and lengthening contractions control the force output during detachment of crossbridges. The force output likely results from the detachment of crossbridges, which explains the decreased activation of muscle relative to force increase or shortening contractions (reduced active formation of crossbridges) (Burnett et al 2000;Christou and Tracy 2005;Kossev and Christova 1998;Laidlaw et al 2000;Nardone and Schieppati 1988). A robust feature of the muscle activation during lengthening contractions is the decrease in the discharge rate of motor units (Kossev and Christova 1998;Laidlaw et al 2000).…”

Section: Phase and Force Variabilitymentioning

confidence: 99%

Motor control differs for increasing and releasing force

Park

Kwon

Solis

et al. 2016

Journal of Neurophysiology

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“…In addition, it has been suggested that the frequency content of the MMG signal may qualitatively reflect the global firing rate of the unfused activated motor units (Orizio 1993;Bichler 2000;Akataki et al 2001Akataki et al , 2003Bichler and Celichowski 2001;Orizio et al 2003). Thus, simultaneous examination of the time and frequency domains of the MMG signal may provide information regarding the unique motor control strategies (recruitment and firing rate) that modulate force production in various muscles (Orizio et al 1989(Orizio et al , 1990Zhang et al 1992;Kossev and Christova 1998;Shinohara et al 1998;Madeleine et al 2001;Linnamo et al 2003;Akataki et al 2003).…”

Section: Mechanomyographymentioning

confidence: 99%

“…Specifically, it has been shown that MMG amplitude is related to motor unit recruitment, while the frequency domain may provide information regarding motor unit firing rate (Orizio 1993;Orizio et al 2003). Thus, simultaneous examination of the time and frequency domains of the MMG signal may be useful for describing the differences that exist in the motor control strategies that modulate force production during isometric versus dynamic muscle actions (Kossev and Christova 1998;Linnamo et al 2003). No studies, however, have examined the MMG and EMG responses during submaximal to maximal, isokinetic muscle actions.…”

Section: Introductionmentioning

confidence: 99%

Mechanomyographic and electromyographic time and frequency domain responses during submaximal to maximal isokinetic muscle actions of the biceps brachii

et al. 2004

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The purpose of this investigation was to determine the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) versus torque relationships during isokinetic muscle actions of the biceps brachii. Twelve adults [mean (SD) age, 22.2 (2.7) years] performed submaximal to maximal isokinetic muscle actions of the dominant forearm flexors. Following determination of isokinetic peak torque (PT), the subjects randomly performed submaximal muscle actions in 20% increments from 20% to 80% PT. Polynomial regression analyses indicated linear increases in both MMG (r2=0.984) and EMG (r2=0.988) amplitude to 100% PT. There were no significant (P>0.05) relationships, however, for MMG and EMG MPF versus isokinetic torque. The results demonstrated similar responses for MMG and EMG in both the time and frequency domains. These findings suggested that simultaneous examination of MMG and EMG amplitude and MPF may be useful for describing the unique motor control strategies that modulate dynamic torque production. Furthermore, the results indicated that dynamic muscle actions can be used when applying techniques that require a linear EMG amplitude versus torque relationship.

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Discharge pattern of human motor units during dynamic concentric and eccentric contractions

Cited by 83 publications

References 38 publications

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

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

Motor control differs for increasing and releasing force

Mechanomyographic and electromyographic time and frequency domain responses during submaximal to maximal isokinetic muscle actions of the biceps brachii

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