Motor unit recruitment during lengthening contractions of human wrist flexors

Stotz, Paula J.; Bawa, Parveen

doi:10.1002/mus.1179

Cited by 48 publications

(30 citation statements)

References 14 publications

(24 reference statements)

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“…Therefore, it is possible that this selective activation may arise through the reciprocal inhibitory pathway between antagonist motor units. It must be acknowledged, however, that although the preferential activation of high threshold motor units has been proposed during lengthening actions (Nardone and Schieppati 1988), similar experiments investigating motor unit recruitment during functional activities have failed to find evidence of a reversal of recruitment order (Jones et al 1994;Stotz and Bawa 2001).…”

Section: Discussionmentioning

confidence: 95%

The force–velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions

2003

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In experiments on isolated animal muscle, the force produced during active lengthening contractions can be up to twice the isometric force, whereas in human experiments lengthening force shows only modest, if any, increase in force. The presence of synergist and antagonist muscle activation associated with human experiments in situ may partly account for the difference between animal and human studies. Therefore, this study aimed to quantify the force-velocity relationship of the human soleus muscle and assess the likelihood that co-activation of antagonist muscles was responsible for the inhibition of torque during submaximal voluntary plantar flexor efforts. Seven subjects performed submaximal voluntary lengthening, shortening(at angular, velocities of +5, -5, +15, -15 and +30, and -30 degrees s(-1)) and isometric plantar flexor efforts against an ankle torque motor. Angle-specific (90 degrees ) measures of plantar flexor torque plus surface and intramuscular electromyography from soleus, medial gastrocnemius and tibialis anterior were made. The level of activation (30% of maximal voluntary isometric effort) was maintained by providing direct visual feedback of the soleus electromyogram to the subject. In an attempt to isolate the contribution of soleus to the resultant plantar flexion torque, activation of the synergist and antagonist muscles were minimised by: (1) flexing the knee of the test limb, thereby minimising the activation of gastrocnemius, and (2) applying an anaesthetic block to the common peroneal nerve to eliminate activation of the primary antagonist muscle, tibialis anterior and the synergist muscles, peroneus longus and peroneus brevis. Plantar flexion torque decreased significantly ( P<0.05) after blocking the common peroneal nerve which was likely due to abolishing activation of the peroneal muscles which are synergists for plantar flexion. When normalised to the corresponding isometric value, the force-velocity relationship between pre- and post-block conditions was not different. In both conditions, plantar flexion torques during shortening actions were significantly less than the isometric torque and decreased at faster velocities. During lengthening actions, however, plantar flexion torques were not significantly different from isometric regardless of angular velocity. It was concluded that the apparent inhibition of lengthening torques during voluntary activation is not due to co-activation of antagonist muscles. Results are presented as mean (SEM).

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Section: Discussionmentioning

confidence: 95%

The force–velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions

2003

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“…As the net muscle force must exceed the load during shortening contractions and be less than the load during lengthening contractions, most studies have reported that discharge rate declines when lowering an inertial load but not when lifting the load (Del Valle and Thomas, 2005;Kallio et al, 2013;Laidlaw et al, 2000;Semmler et al, 2002;Søgaard, 1995;Stotz and Bawa, 2001;Tax et al, 1989). A similar behaviour was observed when resisting instead of assisting a torque motor for a comparable change either in relative force (Altenburg et al, 2009) or in absolute force and fascicle length between the anisometric contractions (Pasquet et al, 2006).…”

Section: Muscle Activation During Submaximal Contractionmentioning

confidence: 87%

“…This selective recruitment of high-threshold motor units ( presumably fastcontracting muscle units) during the lengthening contractions occurred most often at faster angular velocities, which led Nardone and colleagues (1989) to suggest that such changes in task requirements may involve an adjustment in the recruitment order of motor units. Although another paper reported the occasional selective recruitment of high-threshold motor units (3 out of 21 units) in the first dorsal interosseous when lifting and lowering submaximal inertial loads (∼15% MVC force; Howell et al, 1995), most subsequent studies have not found any systematic differences in motor unit recruitment between anisometric contractions when lifting and lowering relatively light inertial loads (≤20% MVC force; Bawa and Jones, 1999;Garland et al, 1996;Laidlaw et al, 2000;Søgaard, 1995;Søgaard et al, 1996;Stotz and Bawa, 2001) or assisting and resisting a torque motor with submaximal forces (≤50% of maximum; Altenburg et al, 2009;Pasquet et al, 2006;Stotz and Bawa, 2001).…”

Section: Muscle Activation During Submaximal Contractionmentioning

confidence: 98%

“…The lower motor unit discharge rates during both maximal (Del Valle and Thomas, 2005) and submaximal (Altenburg et al, 2009;Kallio et al, 2013;Laidlaw et al, 2000;Pasquet et al, 2006;Semmler et al, 2002;Søgaard, 1995;Stotz and Bawa, 2001;Tax et al, 1989) lengthening contractions relative to shortening contractions suggests the involvement of either supraspinal or spinal constraints that limit the neural drive to muscle.…”

Section: Control Of Maximal and Submaximal Lengthening Contractionsmentioning

confidence: 99%

“…In contrast, excitability of the motor neurone pool may be modulated through Renshaw cells (recurrent inhibition; Fig. 5) that may reduce motor unit discharge rate during lengthening contractions (Del Valle and Thomas, 2005;Laidlaw et al, 2000;Pasquet et al, 2006;Semmler et al, 2002;Søgaard et al, 1996;Stotz and Bawa, 2001;Tax et al, 1989). For example, animal experiments have shown that descending pathways can modulate recurrent inhibition and thereby motor unit discharge rate (Baldissera et al, 1981), which could serve as a variable gain regulator for motor output (Hultborn et al, 1979).…”

Section: Spinal Mechanismsmentioning

confidence: 99%

See 2 more Smart Citations

Neural control of lengthening contractions

Duchateau

Enoka

2016

Journal of Experimental Biology

162

181

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A number of studies over the last few decades have established that the control strategy employed by the nervous system during lengthening (eccentric) differs from those used during shortening (concentric) and isometric contractions. The purpose of this review is to summarize current knowledge on the neural control of lengthening contractions. After a brief discussion of methodological issues that can confound the comparison between lengthening and shortening actions, the review provides evidence that untrained individuals are usually unable to fully activate their muscles during a maximal lengthening contraction and that motor unit activity during submaximal lengthening actions differs from that during shortening actions. Contrary to common knowledge, however, more recent studies have found that the recruitment order of motor units is similar during submaximal shortening and lengthening contractions, but that discharge rate is systematically lower during lengthening actions. Subsequently, the review examines the mechanisms responsible for the specific control of maximal and submaximal lengthening contractions as reported by recent studies on the modulation of cortical and spinal excitability. As similar modulation has been observed regardless of contraction intensity, it appears that spinal and corticospinal excitability are reduced during lengthening compared with shortening and isometric contractions. Nonetheless, the modulation observed during lengthening contractions is mainly attributable to inhibition at the spinal level.

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Motor Unit

Heckman

Enoka

2012

Comprehensive Physiology

392

449

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Movement is accomplished by the controlled activation of motor unit populations. Our understanding of motor unit physiology has been derived from experimental work on the properties of single motor units and from computational studies that have integrated the experimental observations into the function of motor unit populations. The article provides brief descriptions of motor unit anatomy and muscle unit properties, with more substantial reviews of motoneuron properties, motor unit recruitment and rate modulation when humans perform voluntary contractions, and the function of an entire motor unit pool. The article emphasizes the advances in knowledge on the cellular and molecular mechanisms underlying the neuromodulation of motoneuron activity and attempts to explain the discharge characteristics of human motor units in terms of these principles. A major finding from this work has been the critical role of descending pathways from the brainstem in modulating the properties and activity of spinal motoneurons. Progress has been substantial, but significant gaps in knowledge remain.

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Motor unit recruitment during lengthening contractions of human wrist flexors

Cited by 48 publications

References 14 publications

The force–velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions

The force–velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions

Neural control of lengthening contractions

Motor Unit

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