The influence of experimental muscle pain on motor unit activity during low-level contraction

Birch, Laila; Christensen, Hanne; Arendt‐Nielsen, Lars; Graven‐Nielsen, Thomas; Søgaard, Karen

doi:10.1007/s004210000279

Cited by 50 publications

(26 citation statements)

References 26 publications

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“…Consistent with our findings, most previous studies (Sohn et al, 2000;Farina et al, 2005;Hodges et al, 2008) have shown decreased motor unit discharge rate during pain when force was maintained. Birch et al (2000) showed no change in discharge rate when averaged across the whole pool, but this could be explained by recruitment of new units and the increase in discharge rates of a few units as identified here.…”

Section: Discussionmentioning

confidence: 51%

“…Consistent with the pain adaptation theory, antagonist muscle activity is increased during pain in some (Arendt-Nielsen et al, 1996;Graven-Nielsen et al, 1997;Svensson et al, 1997;Falla et al, 2007) but not all (Calancie and Bawa, 1986;Birch et al, 2000;Falla et al, 2007) studies. However, to maintain force with decreased motor unit discharge, antagonist muscle activity must decrease.…”

Section: Discussionmentioning

confidence: 75%

“…The most widely accepted "pain adaptation" theory argues that movement amplitude and velocity of the painful segment are reduced by a combination of inhibition of agonist and facilitation of antagonist muscles (Lund et al, 1991). Although many observations during pain have been interpreted to support this theory (Graven-Nielsen et al, 1997;Svensson et al, 1997;Le Pera et al, 2001), others do not (Svensson et al, 1998;Sessle, 1999;Birch et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

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Motor Unit Recruitment Strategies Are Altered during Deep-Tissue Pain

Butler²,

et al. 2009

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Muscle pain is associated with decreased motor unit discharge rate during constant force contractions. As discharge rate is a determinant of force, other adaptations in strategy must explain force maintenance during pain. Our aim was to determine whether motor unit recruitment strategies are altered during pain to maintain force despite reduced discharge rate. Motor unit discharge behavior was recorded in two muscles, one with (quadriceps) and one without [flexor pollicis longus (FPL)] synergists. Motor units were recruited during matched low-force contractions with and without experimentally induced pain, and at higher force without pain. A total of 52 and 34 units were recorded in quadriceps and FPL, respectively, during low-force contractions with and without pain. Of these, 20 quadriceps and 9 FPL units were identified during both trials. The discharge rate of these units reduced during pain in both muscles [quadriceps: 8.7 (1.5) to 7.5 (1.3) Hz, p Ͻ 0.001; FPL: 11.9 (1.5) to 10.0 (1.7) Hz, p Ͻ 0.001]. All remaining units discharged only with or without pain, but not in both conditions. Only one-third of the additional units recruited during pain (quadriceps n ϭ 7/19, FPL n ϭ 3/15) were those expected given orderly recruitment of the motor unit pool as determined during higher-force contractions. We conclude that reduced motor unit discharge rate with pain is accompanied by changes in the population of units used to maintain force. The recruitment of new units is partly inconsistent with generalized inhibition of the motoneuron pool predicted by the "pain adaptation" theory, and provides the basis for a new mechanism of motor adaptation with pain.

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Section: Discussionmentioning

confidence: 51%

Section: Discussionmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

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Motor Unit Recruitment Strategies Are Altered during Deep-Tissue Pain

Butler²,

et al. 2009

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“…As a result, subjects were still able to sustain the same mean level of motor output in both conditions despite significant increases in fluctuations of task-related and tangential forces during painful compared with non-painful conditions. Although inconsistent with the homogeneous inhibition of agonist muscles predicted by the pain-adaptation model (Lund et al 1991), these results are supported by a number of studies which have also reported no pain-induced changes in EMG during static contractions (Graven-Nielsen et al 1997;Birch et al 2000;Hodges et al 2008). …”

Section: Pain-adaptation Strategymentioning

confidence: 67%

Experimental muscle pain increases normalized variability of multidirectional forces during isometric contractions

Salomoni

Graven‐Nielsen

2012

Eur J Appl Physiol

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Pain elicits complex adaptations of motor strategy, leading to impairments in the generation and control of steady forces, which depend on muscle architecture. The present study used a cross-over design to assess the effects of muscle pain on the stability of multidirectional (task-related and tangential) forces during sustained dorsiflexions, elbow flexions, knee extensions, and plantarflexions. Fifteen healthy subjects performed series of isometric contractions (13 s duration, 2.5%, 20%, 50%, 70% of maximal voluntary force) before, during, and after experimental muscle pain. Three-dimensional force magnitude, angle and variability were measured while the task-related force was provided as feedback to the subjects. Surface electromyography was recorded from agonist and antagonist muscles. Pain was induced in agonist muscles by intramuscular injections of hypertonic (6%) saline with isotonic (0.9%) saline injections as control. The pain intensity was assessed on an electronic visual analogue scale (VAS). Experimental muscle pain elicited larger ranges of force angle during knee extensions and plantarflexions (P<0.03) and higher normalized fluctuations of task-related (P<0.02) and tangential forces (P<0.03) compared with control assessments across force levels, while the mean force magnitudes, mean force angle and the level of muscle activity were non-significantly affected by pain. Increased multidirectional force fluctuations probably resulted from multiple mechanisms that, acting together, balanced the mean surface EMG. Although pain adaptations are believed to aim at the protection of the painful site, the current results show that they result in impairments in steadiness of force.

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“…These levels of MVC were chosen because they represent the effort typically performed during most daily activities. 4,15 After a 20-second rest, a strap used to apply the wrist extension force was placed over the palm of the subjects' hand. The extension force was applied by weights, pulling via a cable at an angle 90°with the hand.…”

Section: Procedures Laboratory Setupmentioning

confidence: 99%

A Dynamic Extensor Brace Reduces Electromyographic Activity of Wrist Extensor Muscles in Patients With Lateral Epicondylalgia

Faes¹,

Elk²,

Lint³

et al. 2006

J Orthop Sports Phys Ther

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Study Design: Semiexperimental study. Objective: To investigate the effect of an external wrist extension force on extensor muscle activity during hand gripping in patients with lateral epicondylalgia. Background: Lateral epicondylalgia or ''tennis elbow'' is a common, often disabling ailment affecting millions of people. An optimal treatment strategy remains to be identified. The use of an external wrist extension force may reduce the extensor muscle activity during gripping in these patients. Methods: Muscle activity of the extensor carpi radialis brevis (ECRB), extensor digitorum communis (EDC), and extensor carpi radialis longus (ECRL) was measured using surface EMG. Subjects gripped at an intensity of 10%, 20%, and 30% of the maximum voluntary contraction (MVC) force with and without the dynamic extensor brace and with and without an applied external wrist extension force of 1%, 2%, and 3% of MVC. Results: At all levels of MVC gripping, the EMG signal of the ECRB and EDC were significantly lower for gripping with than without brace. An extension force of 3% of the MVC force significantly reduced the EMG signal of all muscles in almost all measurement conditions. Conclusions: The results of this study indicate that the dynamic extensor brace as well as the external extension force significantly reduced the EMG signal of the wrist extensor muscles during gripping in patients with lateral epicondylalgia. Based on these results, the dynamic extensor brace could be a promising new intervention for lateral epicondylalgia.

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The influence of experimental muscle pain on motor unit activity during low-level contraction

Cited by 50 publications

References 26 publications

Motor Unit Recruitment Strategies Are Altered during Deep-Tissue Pain

Motor Unit Recruitment Strategies Are Altered during Deep-Tissue Pain

Experimental muscle pain increases normalized variability of multidirectional forces during isometric contractions

A Dynamic Extensor Brace Reduces Electromyographic Activity of Wrist Extensor Muscles in Patients With Lateral Epicondylalgia

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