Reflex regulation during sustained and intermittent submaximal contractions in humans

Duchateau, Jacques; Balestra, Costantino; Carpentier, A; Hainaut, Karl

doi:10.1113/jphysiol.2002.016790

Cited by 126 publications

(141 citation statements)

References 40 publications

(86 reference statements)

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“…This effect is likely mediated by presynaptic inhibition of the group Ia afferents rather than by direct inhibitory effects onto the motor neuron pool (Butler et al 2003;Duchateau and Hainaut 1993;Duchateau et al 2002;Ellrich et al 1998;Pettorossi et al 1999;Rossi et al 1999). Additionally, the discharge rate of motor units becomes more variable when local anesthesia presumably blocks fusimotor axons (Hagbarth et al 1986), which might correspond to the greater disfacilitation of group Ia feedback during the position task.…”

Section: Discussionmentioning

confidence: 99%

Motor-Unit Activity Differs With Load Type During a Fatiguing Contraction

Mottram¹,

Jakobi²,

Semmler³

et al. 2005

Journal of Neurophysiology

144

178

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Mottram, Carol J., Jennifer M. Jakobi, John G. Semmler, and Roger M. Enoka. Motor-unit activity differs with load type during a fatiguing contraction. J Neurophysiol 93: [1381][1382][1383][1384][1385][1386][1387][1388][1389][1390][1391][1392] 2005. First published October 13, 2004; doi:10.1152/jn.00837.2004. Despite a similar rate of change in average electromyographic (EMG) activity, previous studies have observed different rates of change in mean arterial pressure, heart rate, perceived exertion, and fluctuations in motor output during the performance of fatiguing contractions that involved different types of loads. To obtain a more direct measure of the motor output from the spinal cord, the purpose of this study was to compare the discharge characteristics of the same motor unit in biceps brachii during the performance of two types of fatiguing contractions. In separate tests with the upper arm vertical and the elbow flexed to 1.57 rad, the seated subjects maintained either a constant upward force at the wrist (force task) or a constant elbow angle (position task) for a prescribed duration. The force and position tasks were performed in random order at a target force equal to 3.5 Ϯ 2.1% (mean Ϯ SD) of the maximal voluntary contraction (MVC) force above the recruitment threshold of the isolated motor unit. Each subject maintained the two tasks for an identical duration (161 Ϯ 96 s) at a mean target force of 22.2 Ϯ 13.4% MVC (range: 3-49% MVC). The dependent variables included the discharge characteristics of the same motor unit in biceps brachii, fluctuations in motor output (force or acceleration), mean arterial pressure, heart rate, and rating of perceived exertion. Despite similar increases in the amplitude of the averaged EMG (% MVC) for the elbow flexor muscles during both tasks (P ϭ 0.60), the rates of increase in mean arterial pressure (P Ͻ 0.001), rating of perceived exertion (P ϭ 0.023), and fluctuations in motor output (P ϭ 0.003) were greater during the position task compared with the force task. Consistent with these differences, mean discharge rate declined at a greater rate during the position task (P ϭ 0.03), and the coefficient of variation for discharge rate increased only during the position task (P ϭ 0.02). Furthermore, more motor units were recruited during the position task compared with the force task (P ϭ 0.01). These findings indicate that despite a comparable net muscle torque, the rate of increase in the motor output from the spinal cord was greater during the position task.

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Section: Discussionmentioning

confidence: 99%

Motor-Unit Activity Differs With Load Type During a Fatiguing Contraction

Mottram¹,

Jakobi²,

Semmler³

et al. 2005

Journal of Neurophysiology

144

178

View full text Add to dashboard Cite

show abstract

“…The EAI declines during fatiguing contractions, as indicated by a decline in the magnitude of the H-reflex (Duchateau et al 2002), whereas the inhibitory afferent feedback increases as a function of metabolite concentration (Bigland-Ritchie et al 1986). The net effect of these changes in afferent input to the motor neuron pool during a sustained contraction is a gradual decline in excitation, which must be compensated by an increase in descending drive to achieve the target force.…”

Section: (C) Neural Adjustments During Sustained Contractionsmentioning

confidence: 99%

Influence of fatigue on the simulated relation between the amplitude of the surface electromyogram and muscle force

Dideriksen

Farina

Enoka

2010

Phil. Trans. R. Soc. A.

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A linear relation between surface electromyogram (EMG) amplitude and muscle force is often assumed and used to estimate the contributions of selected muscles to various tasks. In the presence of muscle fatigue, however, changes in the properties of muscle fibre action potentials and motor unit twitch forces can alter the relation between surface EMG amplitude and force. A novel integrative model of motor neuron control and the generation of muscle fibre action potentials was used to simulate surface EMG signals and muscle force during three fatigue protocols. The change in the simulated relation between surface EMG amplitude and force depended on both the level of fatigue and the details of the fatiguing contraction. In general, surface EMG amplitude overestimated muscle force when fatigue was present. For example, surface EMG amplitudes corresponding to 60 per cent of the amplitude obtained at maximal force without fatigue corresponded to forces in the range 10-40% of the maximal force across three representative fatigue protocols. The results indicate that the surface EMG amplitude cannot be used to predict either the level of muscle activation or the magnitude of muscle force when the muscle exhibits any fatigue.

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“…However, three reasons argue against this hypothesis. First, fatigue is defined as the progressive decline of force during the effort of maintaining maximal (Bigland-Ritchie and Woods, 1984) or low-level voluntary contractions (Duchateau et al, 2002). A progressive decline of force would have resulted in a worse performance during SaD p and SaD u compared with SaR, but all static force periods did not differ significantly with regard to the motor performance.…”

Section: Why Is the Beta-range Coherence Enhanced After Different Dynmentioning

confidence: 99%

Corticospinal Beta-Range Coherence Is Highly Dependent on the Pre-stationary Motor State

Omlor¹,

Patino²,

Méndez-Balbuena³

et al. 2011

J. Neurosci.

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During steady muscle contractions, the human sensorimotor cortex generates oscillations in the beta-frequency range (15-30 Hz) that are coherent with the activity of contralateral spinal motoneurons. This corticospinal coherence is thought to favor stationary motor states, but its mode of operation remains elusive. We hypothesized that corticospinal beta-range coherence depends on the sensorimotor processing state before a steady force task and may thus increase after sensorimotor tuning to dynamic force generation. To test this hypothesis we instructed 16 human subjects to compensate static force after rest as well as after compensating predictable or unpredictable dynamic force with their right index finger. We calculated EEG-EMG coherence, cortical motor spectral power, and the motor performance during the force conditions. Corticospinal beta-coherence during stationary force was excessively elevated if the steadystate contraction was preceded by predictable dynamic force instead of rest, and was highest after unpredictable dynamic force. The beta-power decreased from rest to predictable dynamic force, and was lowest during unpredictable dynamic force. The increase in corticospinal beta-coherence showed a significant negative correlation with the preceding change in beta-power. The tuning to dynamic force did not entail an inferior motor performance during static force. The results imply a correlation between corticospinal beta-range coherence and the computational load of the preceding isometric motor engagement. We suggest beta-range coherence provides a functional corticospinal gateway for steady force-related processing that can override cortical states tuned to dynamic force. The modulation of corticospinal beta-range coherence might thus ensure comparable precision of static force in various motor contexts.

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Reflex regulation during sustained and intermittent submaximal contractions in humans

Cited by 126 publications

References 40 publications

Motor-Unit Activity Differs With Load Type During a Fatiguing Contraction

Motor-Unit Activity Differs With Load Type During a Fatiguing Contraction

Influence of fatigue on the simulated relation between the amplitude of the surface electromyogram and muscle force

Corticospinal Beta-Range Coherence Is Highly Dependent on the Pre-stationary Motor State

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