101
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Simpson M, Burke JR, Davis JM. CUMULATIVE EFFECTS OF INTERMITTENT MAXIMAL CONTRACTIONS ON VOLUNTARY ACTIVATION DEFICITS. Int J Neurosci 2009; 114:671-92. [PMID: 15204059 DOI: 10.1080/00207450490441000] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The purpose of this research was to provide more definitive support for the hypothesis that prolonged muscle activation at high intensities increases voluntary activation deficits. Interpolated twitch responses were evoked during maximal and sub-maximal voluntary contractions of the soleus muscle in 10 college-aged students. Maximal voluntary contractions (MVC), maximal muscle twitches, and interpolated twitch responses were measured before, during, and after fatiguing isometric exercise, five bouts of 20 intermittent MVCs. The relationship between voluntary activation and force was studied by evoking interpolated twitches during sub-maximal voluntary contractions on Day 1 and pre-post fatigue on Day 2. Intraclass reliability coefficients for the MVC, maximal muscle twitch, and interpolated twitch responses were adequate across trials and days (R > or = .80). MVC force and maximal twitch force decreased after the fatiguing exercise bouts by 28% and 32%, respectively (p < .05). Voluntary activation of the fatigue-resistant soleus muscle decreased by 10% after the first five min of maximal exercise with a subsequent decrease of 9% occurring after 25 min of maximal exercise (p < .05). At the end of the experimental session, approximately 30 min after the end of the fatiguing exercise, decreases in 100% MVC force, maximal muscle twitch force, and voluntary activation were still evident: 22%, 23%, and 11%, respectively (p < .05). Post-fatigue, there were also changes in neural strategies for voluntary activation of the soleus muscle at the higher sub-maximal efforts, > or = 70% MVC target levels (p < .05). These data demonstrate the cumulative effects of prolonged exercise on voluntary activation.
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Affiliation(s)
- Michael Simpson
- Department of Exercise Science, School of Public Health, University of South Carolina, Columbia, 29208, USA
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102
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Laurin J, Dousset E, Mesure S, Decherchi P. Neuromuscular recovery pattern after medial collateral ligament disruption in rats. J Appl Physiol (1985) 2009; 107:98-104. [PMID: 19470700 DOI: 10.1152/japplphysiol.00317.2009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The medial collateral ligament (MCL) is one of the most injured ligaments during sport activities. The resulting joint damage effects on neuromuscular system remain unclear. Thus this study was designed to assess the changes in neuromuscular properties of vastus medialis muscle after MCL transection. Complete rupture of MCL was performed on rats, and dynamic functional assessment during locomotion was achieved before and once a week from 1-5 wk postlesion. Twitch properties and metabo- and mechanosensitive afferent fiber responses to specific stimuli were measured 1, 3, and 5 wk after MCL transection. Results indicated that maximum knee angle measured during the stance phase of the gait cycle was decreased during 3 wk after MCL injury and then recovered. Minimum knee angle measured during the stance phase was decreased during 2 wk and showed compensatory effects at week 5. A stepwise decrease in maximum relaxation rate-to-amplitude ratio concomitant with a stepwise increase in half-relaxation time were observed following MCL injury. Variations in metabosensitive afferent response to chemical (KCl and lactic acid) injections were decreased at week 1 and recovered progressively from week 3 to week 5 postlesion. Recovery of the mechanosensitive afferent response to vibrations was not totally complete after 5 wk. Our data indicate that alteration of the sensory pathways from the vastus medialis muscle could be considered as a source of neuromuscular deficits following MCL transection. Our results should be helpful in clinical purpose to improve the knowledge of the influence exerted by ligament rupture on the motor system and permit development of rehabilitation protocols and exercises more appropriate for recovery of functional stability.
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Affiliation(s)
- Jérôme Laurin
- UMR CNRS 6233, Institut des Sciences du Mouvement, Etienne-Jules Marey, Université de la Méditerranée (Aix-Marseille II) Aix-Marseille Université, Parc Scientifique et Technologique de Luminy, Faculté des Sciences du Sport de Marseille, CC910-163, Ave. de Luminy, 13288 Marseille cedex 09, France
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103
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Tillin NA, Bishop D. Factors modulating post-activation potentiation and its effect on performance of subsequent explosive activities. Sports Med 2009; 39:147-66. [PMID: 19203135 DOI: 10.2165/00007256-200939020-00004] [Citation(s) in RCA: 400] [Impact Index Per Article: 26.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Post-activation potentiation (PAP) is induced by a voluntary conditioning contraction (CC), performed typically at a maximal or near-maximal intensity, and has consistently been shown to increase both peak force and rate of force development during subsequent twitch contractions. The proposed mechanisms underlying PAP are associated with phosphorylation of myosin regulatory light chains, increased recruitment of higher order motor units, and a possible change in pennation angle. If PAP could be induced by a CC in humans, and utilized during a subsequent explosive activity (e.g. jump or sprint), it could potentially enhance mechanical power and thus performance and/or the training stimulus of that activity. However, the CC might also induce fatigue, and it is the balance between PAP and fatigue that will determine the net effect on performance of a subsequent explosive activity. The PAP-fatigue relationship is affected by several variables including CC volume and intensity, recovery period following the CC, type of CC, type of subsequent activity, and subject characteristics. These variables have not been standardized across past research, and as a result, evidence of the effects of CC on performance of subsequent explosive activities is equivocal. In order to better inform and direct future research on this topic, this article will highlight and discuss the key variables that may be responsible for the contrasting results observed in the current literature. Future research should aim to better understand the effect of different conditions on the interaction between PAP and fatigue, with an aim of establishing the specific application (if any) of PAP to sport.
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Affiliation(s)
- Neale Anthony Tillin
- School of Human Movement and Exercise Science, the University of Western Australia, Crawley, Western Australia, Australia.
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104
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Pingel J, Moerch L, Kjaer M, Langberg H. The influence of training status on the drop in muscle strength after acute exercise. Eur J Appl Physiol 2009; 106:605-11. [PMID: 19363682 DOI: 10.1007/s00421-009-1055-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/26/2009] [Indexed: 11/30/2022]
Abstract
Skeletal muscles fatigue after exercise, and reductions in maximal force appear. A difference in training status between the legs was introduced by unilateral immobilization of the calf muscles for 2 weeks in young men, who were randomly assigned to two groups, either a RUN group (n = 8) that was exposed to prolonged exercise (1-h running: individual pace) or a REST group (n = 12) that did no exercise after immobilization. Cross-sectional area (CSA) of the triceps-surae muscles was calculated by magnetic resonance imaging (MRI), and maximal voluntary contraction (MVC) force of the plantar flexors was measured before and after immobilization and after the running protocol. The CSA of triceps-surae muscles decreased significantly with a 7% reduction in both groups. A significant drop in the MVC of the triceps-surae muscle (10%; P < 0.05) was observed in response to immobilization. When subjected to running exercise immediately after immobilization, the muscle strength of the triceps-surae muscles dropped even further, but just in the immobilized leg (41%; P < 0.05). The present study highlights the importance of determining the muscle endurance when evaluating the effect of immobilization on muscle parameters.
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Affiliation(s)
- Jessica Pingel
- Institute for Sports Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, Build. 8, 1st floor, 2400 Copenhagen NV, Denmark.
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105
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Lafond D, Champagne A, Descarreaux M, Dubois JD, Prado JM, Duarte M. Postural control during prolonged standing in persons with chronic low back pain. Gait Posture 2009; 29:421-7. [PMID: 19084411 DOI: 10.1016/j.gaitpost.2008.10.064] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2008] [Revised: 10/24/2008] [Accepted: 10/29/2008] [Indexed: 02/02/2023]
Abstract
Prolonged standing has been associated with the onset of low back pain symptoms in working populations. So far, it is unknown how individuals with chronic low back pain (CLBP) behave during prolonged unconstrained standing (PS). The aim of the present study was to analyze the control of posture by subjects with CLBP during PS in comparison to matched healthy adults. The center of pressure (COP) position of 12 CLBP subjects and 12 matched healthy controls was recorded in prolonged standing (30min) and quiet stance tasks (60s) on a force plate. The number and amplitude of COP patterns, the root mean square (RMS), speed, and frequency of COP sway were analyzed. Statistical analyses showed that CLBP subjects produced less postural changes in the antero-posterior direction with decreased postural sway during the prolonged standing task in comparison to the healthy group. Only CLBP subjects were influenced by the prolonged standing task, as demonstrated by their increased COP RMS, COP speed and COP frequency in the quiet standing trial after the prolonged standing task in comparison to the pre-PS trial. The present study provides additional evidence that individuals with CLBP might have altered sensory-motor function. Their inability to generate responses similar to those of healthy subjects during prolonged standing may contribute to CLBP persistence or an increase risk of recurrent back pain episodes. Moreover, quantification of postural changes during prolonged standing could be useful to identify CLBP subjects prone to postural control deficits.
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Affiliation(s)
- Danik Lafond
- Département des sciences de l'activité physique, Université du Québec à Trois-Rivières, Québec, Canada.
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106
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Renggli AS, Verges S, Notter DA, Spengler CM. Development of respiratory muscle contractile fatigue in the course of hyperpnoea. Respir Physiol Neurobiol 2008; 164:366-72. [DOI: 10.1016/j.resp.2008.08.008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2008] [Revised: 08/18/2008] [Accepted: 08/22/2008] [Indexed: 11/29/2022]
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107
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Vuillerme N, Pinsault N, Chenu O, Fleury A, Payan Y, Demongeot J. Postural destabilization induced by trunk extensor muscles fatigue is suppressed by use of a plantar pressure-based electro-tactile biofeedback. Eur J Appl Physiol 2008; 104:119-25. [DOI: 10.1007/s00421-008-0768-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/08/2008] [Indexed: 11/30/2022]
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108
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Dynamic stability control in forward falls: postural corrections after muscle fatigue in young and older adults. Eur J Appl Physiol 2008; 103:295-306. [DOI: 10.1007/s00421-008-0704-z] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/20/2008] [Indexed: 01/26/2023]
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109
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Zwarts M, Bleijenberg G, van Engelen B. Clinical neurophysiology of fatigue. Clin Neurophysiol 2008; 119:2-10. [DOI: 10.1016/j.clinph.2007.09.126] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 09/07/2007] [Accepted: 09/23/2007] [Indexed: 10/22/2022]
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110
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Salavati M, Moghadam M, Ebrahimi I, Arab AM. Changes in postural stability with fatigue of lower extremity frontal and sagittal plane movers. Gait Posture 2007; 26:214-8. [PMID: 17049237 DOI: 10.1016/j.gaitpost.2006.09.001] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2006] [Revised: 06/04/2006] [Accepted: 09/10/2006] [Indexed: 02/02/2023]
Abstract
The purpose of this study was to quantify changes in postural stability with fatigue of the frontal and sagittal movers of the lower extremities. There were four test sessions, with a randomized order assigned according to the muscles tested and the plane of motion. Subjects were 20 healthy men (age: 22.6+/-2.4 years, height: 173.7+/-3.6 cm, weight: 63.3+/-7.9 kg). During each session, one set of muscle groups was fatigued using isokinetic contractions: ankle plantar/dorsi flexors, ankle evertor/invertors, hip flexor/extensors or hip abductor/adductors. The Biodex Stability System was used to assess anterior/posterior and medial/lateral stability before and after muscle fatigue. Repeated measures ANOVAs revealed that fatigue was associated with a significant increase in all stability indices. Fatigue of the hip movers, whether in the frontal or sagittal planes, led to greater increments in stability indices than fatigue of the ankle musculature. Fatigue of the frontal movers resulted in greater increases in the medial/lateral stability index compared to fatigue of the sagittal movers. In conclusion, fatigue of proximal lower extremity muscles affects postural stability and fatigue of the frontal movers is associated with postural instability in the frontal plane.
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Affiliation(s)
- Mahyar Salavati
- University of Social Welfare and Rehabilitation Sciences, Tehran, Iran
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111
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Vuillerme N, Anziani B, Rougier P. Trunk extensor muscles fatigue affects undisturbed postural control in young healthy adults. Clin Biomech (Bristol, Avon) 2007; 22:489-94. [PMID: 17346866 DOI: 10.1016/j.clinbiomech.2007.01.007] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/13/2004] [Revised: 01/19/2007] [Accepted: 01/23/2007] [Indexed: 02/07/2023]
Abstract
BACKGROUND The purpose of this study was to investigate the effects of trunk extensor muscles fatigue on undisturbed postural control in young healthy adults. METHODS Fifteen university students were asked to stand upright as immobile as possible with their eyes closed in two conditions of Fatigue and No fatigue of the trunk extensor muscles. Muscular fatigue was achieved by performing trunk repetitive extensions until maximal exhaustion. Centre of foot pressure displacements, recorded using a force platform, were used to compute the motions of the vertical projection of the centre of gravity and those of the difference between the centre of pressure and those of the difference between the centre of pressure and the vertical projection of the centre of gravity. These motions were processed through space-time and frequency domain analyses. FINDINGS Larger centre of pressure minus centre of gravity and centre of gravity motions in the Fatigue than No fatigue condition are observed along both the medio-lateral and antero-posterior axes, this effect being more accentuated along the antero-posterior axis. INTERPRETATION The present findings suggest that trunk extensor muscles fatigue deteriorates undisturbed stance control, yielding, along the antero-posterior axis mainly, (1) a greater neuromuscular requirements for ensuring standing control, as indicated by the increased centre of pressure minus centre of gravity motions, and (2) a deterioration of postural performance, as indicated by the increased centre of gravity motions.
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Affiliation(s)
- Nicolas Vuillerme
- Laboratoire TIMC-IMAG, UMR CNRS 5525, Faculté de Médecine, 38706 La Tronche cédex, France.
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112
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Kavanagh JJ, Morrison S, Barrett RS. Lumbar and cervical erector spinae fatigue elicit compensatory postural responses to assist in maintaining head stability during walking. J Appl Physiol (1985) 2006; 101:1118-26. [PMID: 16763109 DOI: 10.1152/japplphysiol.00165.2006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The purpose of this study was to examine how inducing fatigue of the 1) lumbar erector spinae and 2) cervical erector spinae (CES) muscles affected the ability to maintain head stability during walking. Triaxial accelerometers were attached to the head, upper trunk, and lower trunk to measure accelerations in the vertical, anterior-posterior, and mediolateral directions during walking. Using three accelerometers enabled two adjacent upper body segments to be defined: the neck segment and trunk segment. A transfer function was applied to root mean square acceleration, peak power, and harmonic data derived from spectral analysis of accelerations to quantify segmental gain. The structure of upper body accelerations were examined using measures of signal regularity and smoothness. The main findings were that head stability was only affected in the anterior-posterior direction, as accelerations of the head were less regular following CES fatigue. Furthermore, following CES fatigue, the central nervous system altered the attenuation properties of the trunk segment in the anterior-posterior direction, presumably to enhance head stability. Following lumbar erector spinae fatigue, the trunk segment had greater gain and increased regularity and smoothness of accelerations in the mediolateral direction. Overall, the results of this study suggest that erector spinae fatigue differentially altered segmental attenuation during walking, according to the level of the upper body that was fatigued and the direction that oscillations were attenuated. A compensatory postural response was not only elicited in the sagittal plane, where greater segmental attenuation occurred, but also in the frontal plane, where greater segmental gain occurred.
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Affiliation(s)
- Justin J Kavanagh
- School of Physiotherapy and Exercise Science, Griffith University, PMB 50, Gold Coast Mail Centre, Queensland, Australia 9726.
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113
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Apriantono T, Nunome H, Ikegami Y, Sano S. The effect of muscle fatigue on instep kicking kinetics and kinematics in association football. J Sports Sci 2006; 24:951-60. [PMID: 16882629 DOI: 10.1080/02640410500386050] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The aim of this study was to examine the effect of leg muscle fatigue on the kinetics and kinematics of the instep football kick. Fatigue was induced by repeated, loaded knee extension (40% body weight) and flexion (50% body weight) motions on a weight-training machine until exhaustion. The kicking motions of seven male players were captured three-dimensionally at 500 Hz before and immediately after the fatigue protocol. The significantly slower ball velocity observed in the fatigue condition was due to both reduced lower leg swing speed and poorer ball contact. The reduced leg swing speed, represented by a slower toe linear velocity immediately before ball impact and slower peak lower leg angular velocity, was most likely due to a significantly reduced resultant joint moment and motion-dependent interactive moment during kicking. These results suggest that the specific muscle fatigue induced in the present study not only diminished the ability to generate force, but also disturbed the effective action of the interactive moment leading to poorer inter-segmental coordination during kicking. Moreover, fatigue obscured the eccentric action of the knee flexors immediately before ball impact. This might increase the susceptibility to injury.
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114
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Schillings ML, Kalkman JS, van der Werf SP, Bleijenberg G, van Engelen BGM, Zwarts MJ. Central adaptations during repetitive contractions assessed by the readiness potential. Eur J Appl Physiol 2006; 97:521-6. [PMID: 16718505 DOI: 10.1007/s00421-006-0211-z] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/31/2006] [Indexed: 11/29/2022]
Abstract
Physiological fatigue, a loss of maximal force producing capacity, may originate both from changes at the peripheral and at the central level. The readiness potential (RP) provides a measure to study adaptations to physiological fatigue at the motor cortex. We have studied the RP in the course of repetitive contractions at a high force level. Fourteen female healthy subjects made repetitive force grip contractions at 70% of their maximal voluntary contraction (MVC) for 30 min. Contractions were self-paced and inter-squeeze interval was about 7 s. During the repetitive contractions, the area under the curve of the RP almost doubled at electrode Cz and increased fourfold at electrodes C3' and C4'. The onset of negativity moved forward from 1.5 to 1.9 s before force onset at Cz and from 1.0 to 1.6 s and 1.7 s before force onset at C3' and C4', respectively. EMG amplitude and median frequency did not change significantly and MVC after the fatiguing exercise was 93% of MVC before, indicating relatively little physiological fatigue. The increase of the RP during the repetitive contractions is clearly in excess of the almost absent signs of peripheral fatigue. Because the increase of the RP does not lead to an increased force production, we propose that it is a central adaptation counteracting the decrease of cortical efficiency during repetitive contractions.
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Affiliation(s)
- M L Schillings
- Department of Clinical Neurophysiology, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
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115
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Silva BARS, Martinez FG, Pacheco AM, Pacheco I. Efeitos da fadiga muscular induzida por exercícios no tempo de reação muscular dos fibulares em indivíduos sadios. REV BRAS MED ESPORTE 2006. [DOI: 10.1590/s1517-86922006000200006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A fadiga muscular (FM) é um fenômeno comum nas atividades esportivas e diárias, resultando numa piora da performance motora. Ela é considerada um dos fatores causadores de lesões músculo-esqueléticas. A entorse de tornozelo é um exemplo: a FM afetaria tanto o sistema aferente quanto o eferente. Vários estudos têm analisado a influência da FM no controle neuromuscular (CNM); entretanto, existe pouca pesquisa sobre essa influência na velocidade de reação dos músculos. O objetivo deste estudo foi verificar os efeitos da FM no tempo de reação muscular (TRM) dos músculos fibulares, que são os primeiros a responder a um estresse em inversão do tornozelo. Foram estudados 14 indivíduos saudáveis masculinos (idade: 20-35 anos), que tiveram seus TRM avaliados por meio de eletromiografia (EMG) de superfície. O início da atividade muscular foi definido como a média de repouso + 3x o desvio-padrão (DP). O TRM dos fibulares foi mensurado após uma inversão súbita de 20º realizada numa plataforma. A inversão súbita foi realizada antes e depois da fadiga muscular, que foi induzida por exercícios localizados dos fibulares até a exaustão. Os resultados mostraram que houve um aumento significativo do tempo de reação muscular após a fadiga (p < 0,01). Durante atividades esportivas prolongadas e durante o processo de reabilitação, deve-se ter cautela na realização de tarefas que requeiram respostas musculares extremamente rápidas sob condições de fadiga muscular.
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Affiliation(s)
| | | | | | - Ivan Pacheco
- UFRGS; Clube Grêmio Náutico União; Federação Gaúcha de Futevôlei
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116
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Abstract
Weakness is a characteristic of muscles influenced by the postpolio syndrome (PPS), amyotrophic lateral sclerosis (ALS), and spinal cord injury (SCI). The strength deficits relate to changes in muscle use and to the chronic denervation that can follow the spinal motoneuron death common to these disorders. PPS, ALS, and SCI also involve variable amounts of supraspinal neuron death, the effects of which on muscle weakness remains unclear. Nevertheless, weakness of muscle itself defines the functional consequences of these disorders. A weaker muscle requires an individual to work that muscle at higher than usual intensities relative to its maximal capacity, inducing progressive fatigue and an increased sense of effort. Little evidence is available to suggest that the fatigue commonly experienced by individuals with these disorders relates to an increase in the intrinsic fatigability of the muscle fibers. The only exception is when SCI induces chronic muscle paralysis. To reduce long-term functional deficits in these disorders, studies must identify the signaling pathways that influence neuron survival and determine the factors that encourage and limit sprouting of motor axons. This may ensure that a greater proportion of the fibers in each muscle remain innervated and available for use.
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Affiliation(s)
- Christine K Thomas
- The Miami Project to Cure Paralysis, Lois Pope LIFE Center, 1095 NW 14th Terrace (R-48), Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
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117
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Ge HY, Arendt-Nielsen L, Farina D, Madeleine P. Gender-specific differences in electromyographic changes and perceived pain induced by experimental muscle pain during sustained contractions of the upper trapezius muscle. Muscle Nerve 2006; 32:726-33. [PMID: 16136601 DOI: 10.1002/mus.20410] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The aim of the study was to investigate gender-specific differences in the pain-induced alterations of muscle activity during sustained contractions of the upper trapezius muscle. Surface electromyographic (EMG) signals were recorded bilaterally from the upper trapezius muscles of healthy volunteers (10 men and 9 women). The subjects held the arms at 90 degrees abduction for 5 s (short contraction) and 3 min (sustained contraction). These contractions were performed before, during, and after injection of 0.5 ml of hypertonic saline (5.8%) bilaterally in the upper trapezius muscles. Injection of isotonic saline (0.9%) served as control. The root mean square (RMS) and mean power frequency (MPF) were computed from the EMG signals and normalized to the values obtained during maximal voluntary contractions. In the short contractions, injection of hypertonic saline, but not isotonic saline, induced a less pronounced decrease in RMS in women than men, and a significant decrease in MPF in men but not women. In the sustained contractions, RMS slope increased and MPF slope decreased (less negative) with muscle pain in men but not women. It was concluded that the pain-induced changes in motor control strategies during sustained contractions differ in men and women, which may partly explain gender differences in the incidence of musculoskeletal pain.
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Affiliation(s)
- Hong-You Ge
- Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7 D-3, DK-9220, Aalborg, Denmark
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118
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Saey D, Côté CH, Mador MJ, Laviolette L, LeBlanc P, Jobin J, Maltais F. Assessment of muscle fatigue during exercise in chronic obstructive pulmonary disease. Muscle Nerve 2006; 34:62-71. [PMID: 16583366 DOI: 10.1002/mus.20541] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Contractile fatigue is associated with exercise intolerance in patients with chronic obstructive pulmonary disease (COPD). Contractile fatigue may be assessed by quantifying the decline in strength after a fatiguing protocol but this may pose practical problems. The purpose of this study was to investigate the relationship between the decline in quadriceps strength, quadriceps electrical activity, perception of leg fatigue, and arterial lactate level in patients with COPD during constant work-rate cycling exercise. The decline in quadriceps strength was significantly associated with the decrease in electromyographic median frequency (r = 0.606), leg fatigue perception (r = 0.453), and arterial lactate level (r = 0.384). Using the receiver-operating-characteristic curve, it was found that a 4% decline in electromyographic median frequency had a 94% sensitivity and a 75% specificity to predict contractile fatigue. We conclude that contractile fatigue commonly occurs during cycling exercise in COPD. The electromyographic median frequency appears to be a valuable indirect marker to predict contractile leg fatigue.
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Affiliation(s)
- Didier Saey
- Centre de Recherche, Hôpital Laval, Institut Universitaire de Cardiologie et de Pneumologie de l'Université Laval, 2725 Chemin Ste-Foy, Québec G1V 4G5, Canada
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119
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Babault N, Desbrosses K, Fabre MS, Michaut A, Pousson M. Neuromuscular fatigue development during maximal concentric and isometric knee extensions. J Appl Physiol (1985) 2005; 100:780-5. [PMID: 16282433 DOI: 10.1152/japplphysiol.00737.2005] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study aimed to investigate mechanisms of neuromuscular fatigue during maximal concentric and isometric leg extensions inducing similar torque decrements. Nine physically active men performed two separate fatiguing sessions maintained until similar torque decreases were obtained. The first session, only conducted under isokinetic concentric conditions (CON), consisted of three series of 30 maximal voluntary concentric knee extensions (60 degrees/s). The second session, exclusively isometric (ISO), mimicked the torque decreases registered during the CON session while performing three long-lasting ISO contractions. Maximal voluntary torque, activation level (twitch interpolation technique), electromyographic activity (root mean square and median frequency) of the vastus lateralis muscle, and electrically evoked doublet-twitch mechanical properties were measured before and at the end of each of the three series. After the three series, similar torque decrements were obtained for both fatiguing procedures. The total fatiguing contraction durations were not different among procedures. With equivalent voluntary torque decrements, the doublet-twitch amplitude reduction was significantly greater (P<0.01) during the two first series of the CON procedure compared with ISO. No difference was observed for the third series. Although no difference was recorded with fatigue for median frequency changes between CON and ISO, activation levels and root mean square values demonstrated greater reductions (P<0.05) for all three series during the ISO procedure compared with CON. Performing CON or ISO fatiguing exercises demonstrated different fatigue origins. With CON exercises, peripheral fatigue developed first, followed by central fatigue, whereas with ISO exercises the fatigue pattern was inverted.
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Affiliation(s)
- Nicolas Babault
- Performance Motrice et Santé, Unité de Formation et de Recherche des Sciences et Techniques des Activités Physiques et Sportives, Université Marc Bloch, 14 rue René Descartes, 67084 Strasbourg Cedex, France.
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120
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Bambaeichi E, Reilly T, Cable NT, Giacomoni M. Influence of time of day and partial sleep loss on muscle strength in eumenorrheic females. ERGONOMICS 2005; 48:1499-511. [PMID: 16338716 DOI: 10.1080/00140130500101437] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Disrupted sleep is the most common form of sleep deprivation in travellers, shift workers, athletes the night before important competitions and among parents of infants. The influence of partial sleep loss on muscle strength might differ according to the time of testing on the following day. This study was therefore designed to assess the interaction between the effects of partial sleep loss and time of day on muscle strength in females. Eight sedentary eumenorrheic females (mean +/- SD; age 30 +/- 6 years, height 1.62 +/- 0.06 m and body mass 67 +/- 5.0 kg) took part in the study, in a counterbalanced design. Measurements of muscle strength were carried out at 06:00 and 18:00 hours after the one control night (no sleep loss) and the one night of partial sleep loss, during menses. Muscle strength measures included isokinetic (at 1.05, 3.14 rad s(-1); 90 degrees range of motion) and isometric peak torque (at 60 degrees of knee flexion) of knee extensors and flexors (dominant leg). In addition, isometric force of knee extensors with super-imposed electrical twitches (50 Hz, 250 V, 200 mus pulse width) was measured using the same procedure in order to control for motivation. Rectal temperature was measured during the 30 min before muscle strength measurements. Partial sleep loss consisted of allowing 2.5 h sleep (between 03:00 and 05:30 h), whilst in the control condition (no sleep loss) subjects retired between 22:30 and 23:30 h, rising at 05:30 hours. All measurements were conducted at just one phase of the menstrual cycle (menses) to prevent any masking effect due to different phases of the menstrual cycle. In both conditions (with and without partial sleep loss) a diurnal variation was observed in peak torque of knee flexors at 1.05 (F(1,7) = 5.5, p < 0.05) and 3.14 rad s(-1) (F(1,7) = 8.0, p < 0.05); values at 18:00 hours were 4.5 and 5.9% higher than at 06:00 hours, respectively. No significant diurnal variation was observed for the other muscle strength measures. No significant effect of partial sleep loss or interaction effect (sleep x time of day) was observed for muscle strength measures. However, the performance rhythms were in phase with the circadian rhythm in rectal temperature. Partial sleep deprivation over one night did not have any adverse effect on maximal muscle strength, nor on diurnal variations of muscle strength indices. As the effect of time of day was observed with some of the muscle strength measures, it is suggested that, in designing future studies using females, the control of time of day is essential.
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Affiliation(s)
- E Bambaeichi
- Department of Physical Education, Isfahan University, Iran.
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121
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Morrison S, Kavanagh J, Obst SJ, Irwin J, Haseler LJ. The effects of unilateral muscle fatigue on bilateral physiological tremor. Exp Brain Res 2005; 167:609-21. [PMID: 16078030 DOI: 10.1007/s00221-005-0050-x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2005] [Accepted: 05/05/2005] [Indexed: 11/28/2022]
Abstract
The aim of this study was to examine the post-exercise effects of fatiguing the wrist extensor muscles of a single arm on postural tremor and muscle activity in both arms. Previous research has shown that, for neurologically normal subjects, the tremor seen within a single limb segment is uncorrelated to that seen contralaterally. However it has been speculated that some bilateral relation does exist, and that the nature of the relation may only become evident under conditions where the neuromuscular system is perturbed. To further investigate this potential bilateral relation, seven healthy subjects were required to adopt a bilateral postural pointing position after exercise-induced fatigue of the wrist extensor muscles of a single arm. Tremor from the forearm, hand and finger segments of each arm, surface EMG activity from extensor digitorum (ED) of each arm, and blood lactate data were collected prior to and after the exercise intervention. The main result was that fatiguing the distal muscles of one arm resulted in a bilateral increase in both the physiological tremor and ED activity. The change in tremor was confined to the index finger with no change in the tremor for the hand or forearm segments of either arm. While three peaks were seen in the frequency profile of the finger tremor, the effects of fatigue were confined to an increase in the peak power of the neurally generated 8-12 Hz tremor component. The contralateral increase in muscle activity was also reflected by a change in the frequency profile of the EMG output, with an increase in the peak power of both muscles following exercise of the wrist extensors of a single arm. The bilateral increases in physiological tremor and EMG activity of ED were only observed during the bilateral pointing task, with no changes in tremor or EMG activity seen for the non-exercised limb during the unilateral exercise protocol. The specificity of the resultant increases in the neurally generated 8-12 Hz component of finger tremor amplitude and EMG activity, coupled with the lack of any changes in tremor for the more proximal arm segments, indicate that these bilateral effects were mediated by an increase in the central neural drive to both limbs. Together this set of results challenges the general assumption of bilateral independence of tremor production, and further illustrate the task dependent nature of exercise-induced fatigue.
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Affiliation(s)
- S Morrison
- School of Physiotherapy and Exercise Science, Gold Coast Campus Griffith University, PMB 50 Gold Coast Mail Centre, QLD 9276, Australia.
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122
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Guillot A, Haguenauer M, Dittmar A, Collet C. Effect of a fatiguing protocol on motor imagery accuracy. Eur J Appl Physiol 2005; 95:186-90. [PMID: 16003536 DOI: 10.1007/s00421-005-1400-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/13/2005] [Indexed: 10/25/2022]
Abstract
This study was devised to evaluate the influence of muscle fatigue on athletes' ability to perform motor imagery. Performance impairment is a consequence of fatigue, but alterations on perception and mental activity may also occur. To test whether peripheral fatigue affects mental processes, ten sports students imagined three consecutive countermovement jumps before and after a fatiguing protocol, through repetition of upright movements, at 70% of maximal voluntary contraction, until exhaustion. Autonomic nervous system responses and imagined movement durations were considered the dependent variables. Actual duration was systematically overestimated during both visual and kinesthetic imagery, but motor imagery duration and autonomic responses were similar without and under fatigue. Results suggest that muscle fatigue, unlike fatigue induced by prolonged exercise, does not elicit mental fatigue and therefore does not alter motor imagery accuracy.
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Affiliation(s)
- Aymeric Guillot
- Centre de Recherche et d'Innovation sur le Sport, Université Claude Bernard Lyon I, Villeurbanne, France.
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123
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Vuillerme N, Pinsault N, Vaillant J. Postural control during quiet standing following cervical muscular fatigue: effects of changes in sensory inputs. Neurosci Lett 2005; 378:135-9. [PMID: 15781146 DOI: 10.1016/j.neulet.2004.12.024] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2004] [Revised: 12/09/2004] [Accepted: 12/09/2004] [Indexed: 11/24/2022]
Abstract
The purpose of the present experiment was to investigate the effects of cervical muscular fatigue on postural control during quiet standing under different conditions of reliability and/or availability of somatosensory inputs from the plantar soles and the ankles and visual information. To this aim, 14 young healthy adults were asked to sway as little as possible in three sensory conditions (No vision, No vision-Foam support and Vision) executed in two conditions of No fatigue and Fatigue of the scapula elevator muscles. Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed that (1) the cervical muscular fatigue yielded increased CoP displacements in the absence of vision, (2) this effect was more accentuated when somatosensation was degraded by standing on a foam surface and (3) the availability of vision allowed the individuals to suppress this destabilising effect. On the whole, these findings not only stress the importance of intact cervical neuromuscular function on postural control during quiet standing, but also suggest a reweigthing of sensory cues in balance control following cervical muscular fatigue by increasing the reliance on the somatosensory inputs from the plantar soles and the ankles and visual information.
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Affiliation(s)
- Nicolas Vuillerme
- Laboratoire de Modélisation des Activités Sportives, Université de Savoie, Domaine Universitaire, 73376 Le Bourget du Lac cédex, France.
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124
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Evidence for complex system integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans. Br J Sports Med 2005; 38:797-806. [PMID: 15562183 DOI: 10.1136/bjsm.2003.009852] [Citation(s) in RCA: 283] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
A model is proposed in which the development of physical exhaustion is a relative rather than an absolute event and the sensation of fatigue is the sensory representation of the underlying neural integrative processes. Furthermore, activity is controlled as part of a pacing strategy involving active neural calculations in a "governor" region of the brain, which integrates internal sensory signals and information from the environment to produce a homoeostatically acceptable exercise intensity. The end point of the exercise bout is the controlling variable. This is an example of a complex, non-linear, dynamic system in which physiological systems interact to regulate activity before, during, and after the exercise bout.
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125
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Korotkov A, Radovanovic S, Ljubisavljevic M, Lyskov E, Kataeva G, Roudas M, Pakhomov S, Thunberg J, Medvedev S, Johansson H. Comparison of brain activation after sustained non-fatiguing and fatiguing muscle contraction: a positron emission tomography study. Exp Brain Res 2005; 163:65-74. [PMID: 15645226 DOI: 10.1007/s00221-004-2141-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2004] [Accepted: 10/13/2004] [Indexed: 10/25/2022]
Abstract
The concept of fatigue refers to a class of acute effects that can impair motor performance, and not to a single mechanism. A great deal is known about the peripheral mechanisms underlying the process of fatigue, but our knowledge of the roles of the central structures in that process is still very limited. During fatigue, it has been shown that peripheral apparatus is capable of generating adequate force while central structures become insufficient/sub-optimal in driving them. This is known as central fatigue, and it can vary between muscles and different tasks. Fatigue induced by submaximal isometric contraction may have a greater central component than fatigue induced by prolonged maximal efforts. We studied the changes in regional cerebral blood flow (rCBF) of brain structures after sustained isometric muscle contractions of different submaximal force levels and of different durations, and compared them with the conditions observed when the sustained muscle contraction becomes fatiguing. Changes in cortical activity, as indicated by changes in rCBF, were measured using positron emission tomography (PET). Twelve subjects were studied under four conditions: (1) rest condition; (2) contraction of the m. biceps brachii at 30% of MVC, sustained for 60 s; (3) contraction at 30% of MVC, sustained for 120 s, and; (4) contraction at 50% of MVC, sustained for 120 s. The level of rCBF in the activated cortical areas gradually increased with the level and duration of muscle contraction. The fatiguing condition was associated with predominantly contralateral activation of the primary motor (MI) and the primary and secondary somatosensory areas (SI and SII), the somatosensory association area (SAA), and the temporal areas AA and AI. The supplementary motor area (SMA) and the cingula were activated bilaterally. The results show increased cortical activation, confirming that increased effort aimed at maintaining force in muscle fatigue is associated with increased activation of cortical neurons. At the same time, the activation spread to several cortical areas and probably reflects changes in both excitatory and inhibitory cortical circuits. It is suggested that further studies aimed at controlling afferent input from the muscle during fatigue may allow a more precise examination of the roles of each particular region involved in the processing of muscle fatigue.
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Affiliation(s)
- Alexander Korotkov
- Center for Musculoskeletal Research, University of Gävle, Petrus Laestadius väg, Box 7629, 907 13 Umeå, Sweden
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126
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Schmid M, Schieppati M. Neck muscle fatigue and spatial orientation during stepping in place in humans. J Appl Physiol (1985) 2004; 99:141-53. [PMID: 15489256 DOI: 10.1152/japplphysiol.00494.2004] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Neck proprioceptive input, as elicited by muscle vibration, can produce destabilizing effects on stance and locomotion. Neck muscle fatigue produces destabilizing effects on stance, too. Our aim was to assess whether neck muscle fatigue can also perturb the orientation in space during a walking task. Direction and amplitude of the path covered during stepping in place were measured in 10 blindfolded subjects, who performed five 30-s stepping trials before and after a 5-min period of isometric dorsal neck muscle contraction against a load. Neck muscle electromyogram amplitude and median frequency during the head extensor effort were used to compute a fatigue index. Head and body kinematics were recorded by an optoelectronic system, and stepping cadence was measured by sensorized insoles. Before the contraction period, subjects normally stepped on the spot or drifted forward. After contraction, some subjects reproduced the same behavior, whereas others reduced their forward progression or even stepped backward. The former subjects showed minimal signs of fatigue and the latter ones marked signs of fatigue, as quantified by the dorsal neck electromyogram index. Head position and cadence were unaffected in either group of subjects. We argue that the abnormal fatigue-induced afferent input originating in the receptors transducing the neck muscle metabolic state can modulate the egocentric spatial reference frame. Notably, the effects of neck muscle fatigue on orientation are opposite to those produced by neck proprioception. The neck represents a complex source of inputs capable of modifying our orientation in space during a locomotor task.
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Affiliation(s)
- Micaela Schmid
- Human Movement Laboratory, Centro Studi Attività Motorie, Fondazione Salvatore Maugeri, Istituto Scientifico di Pavia, Via Ferrata 8, I-27100 Pavia, Italy
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127
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Abstract
We hypothesised that, since anomalous neck proprioceptive input can produce perturbing effects on posture, neck muscle fatigue could alter body balance control through a mechanism connected to fatigue-induced afferent inflow. Eighteen normal subjects underwent fatiguing contractions of head extensor muscles. Sway during quiet stance was recorded by a dynamometric platform, both prior to and after fatigue and recovery, with eyes open and eyes closed. After each trial, subjects were asked to rate their postural control. Fatigue was induced by having subjects stand upright and exert a force corresponding to about 35% of maximal voluntary effort against a device exerting a head-flexor torque. The first fatiguing period lasted 5 min (F1). After a 5-min recovery period (R1), a second period of fatiguing contraction (F2) and a second period of recovery (R2) followed. Surface EMG activity from dorsal neck muscles was recorded during the contractions and quiet stance trials. EMG median frequency progressively decreased and EMG amplitude progressively increased during fatiguing contractions, demonstrating that muscle fatigue occurred. After F1, subjects swayed to a larger extent compared with control conditions, recovering after R1. Similar findings were obtained after F2 and after R2. Although such behaviour was detectable under both visual conditions, the effects of fatigue reached significance only without vision. Subjective scores of postural control diminished when sway increased, but diminished more, for equal body sway, after fatigue and recovery. Contractions of the same duration, but not inducing EMG signs of fatigue, had much less influence on body sway or subjective scoring. We argue that neck muscle fatigue affects mechanisms of postural control by producing abnormal sensory input to the CNS and a lasting sense of instability. Vision is able to overcome the disturbing effects connected with neck muscle fatigue.
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Affiliation(s)
- M Schieppati
- Department of Experimental Medicine, Section of Human Physiology, University of Pavia, Pavia, Italy.
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128
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Corbeil P, Blouin JS, Bégin F, Nougier V, Teasdale N. Perturbation of the postural control system induced by muscular fatigue. Gait Posture 2003; 18:92-100. [PMID: 14654212 DOI: 10.1016/s0966-6362(02)00198-4] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In this experiment, we induced muscular fatigue of ankle plantar-flexors to examine how it deteriorates the regulation of bipedal quiet upright standing. Postural stability was assessed in conditions with and without vision over 60 s period to examine not only classical postural variables (time- and frequency-domain analyses), but also structural variables (stabilogram-diffusion analysis). Muscular fatigue was induced with repeated plantar-flexion of both legs. With muscular fatigue, subjects exhibited an increased postural sway (faster center of pressure (CP) velocity, and greater CP mean and median frequency) and a decreased long-term scaling exponent compared with the control conditions. The fatigue conditions, however, did not modify the range of oscillations and the variability of the postural oscillations around the mean position of CP. The effects of muscular fatigue were similar with eyes open and eyes closed. These results suggest that fatigue did induce some changes in the control mode of postural stability, but the detection/action capabilities of the sensorimotor system remained partly efficient when the ankle plantar-flexors were fatigued. Furthermore, the decreased long-term scaling exponent observed with fatigue suggests that the control of upright stance operates in a less stochastic and more antipersistent manner when fatigue is present (i.e. past and future behaviors were more negatively correlated and thus more tightly regulated). Altogether, the present results suggest that, compared with the no-fatigue conditions, fatigue places higher demands on the postural control system by increasing the frequency of actions needed to regulate the upright stance.
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Affiliation(s)
- Philippe Corbeil
- Faculté de Médecine, Division de Kinésiologie, PEPS, Université Laval, Québec, Que, Canada G1K 7P4
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129
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Andersen B, Westlund B, Krarup C. Failure of activation of spinal motoneurones after muscle fatigue in healthy subjects studied by transcranial magnetic stimulation. J Physiol 2003; 551:345-56. [PMID: 12824449 PMCID: PMC2343163 DOI: 10.1113/jphysiol.2003.043562] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
During a sustained maximal effort a progressive decline in the ability to drive motoneurones (MNs) develops. We used the recently developed triple stimulation technique (TST) to study corticospinal conduction after fatiguing exercise in healthy subjects. This method employs a collision technique to estimate the proportion of motor units activated by a transcranial magnetic stimulus. Following a sustained contraction of the abductor digiti minimi muscle at 50 % maximal force maintained to exhaustion there was an immediate reduction of the TST response from > 95 % to about 60 %. This effect recovered to control levels within 1 min and implies that a decreased number of spinal MNs were excited. Additional TST experiments after maximal and submaximal efforts showed that the decrease in size of the TST response was related to duration and strength of exercise. Motor evoked potentials (MEPs) after conventional transcranial magnetic stimulation (TMS) and responses to peripheral nerve stimulation were recorded following the same fatigue protocol. The size of both the MEPs and the peripheral responses increased after the contraction and were in direct contrast to the decrease in size of the TST response. This points to increased probability of repetitive spinal MN activation during fatigue even if some MNs in the pool failed to discharge. Silent period duration following cortical stimulation lengthened by an average of 55 ms after the contraction and recovered within a time course similar to that of the TST response depression. Overall, the results suggest that the outflow from the motor cortex could become insufficient to drive all spinal MNs to discharge when the muscle is fatigued and that complex interactions between failure of activation and compensatory mechanisms to maintain motor unit activation occur during sustained voluntary activity. When inability to maintain force occurs during submaximal effort, failure of activation of motor units is predominant.
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Affiliation(s)
- Birgit Andersen
- Department of Clinical Neurophysiology 3063, Rigshospitalet, Copenhagen University Hospital, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
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130
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Butler JE, Thomas CK. Effects of sustained stimulation on the excitability of motoneurons innervating paralyzed and control muscles. J Appl Physiol (1985) 2003; 94:567-75. [PMID: 12391058 DOI: 10.1152/japplphysiol.01176.2001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The excitability of thenar motoneurons (reflected by F-wave persistence and amplitude) and thenar muscle force were measured during a stimulation protocol (90 s of 18-Hz supramaximal electrical stimulation of the median nerve) designed to induce muscle fatigue (force decline). Data from muscles (n = 15) paralyzed by chronic cervical spinal cord injury were compared with those obtained from control muscles (n = 6). The persistence of F waves in both paralyzed and control muscles increased from approximately 60 to approximately 76% during the first 10 s of the fatigue protocol. Persistence then declined progressively to approximately 33% at 90 s. These changes in F-wave persistence suggest that similar reductions occur in the excitability of the motoneurons to paralyzed and control motor units after sustained antidromic activation. Despite this, significantly larger force declines occurred in the paralyzed muscles of spinal cord-injured subjects (approximately 60%) than in the muscles of control subjects (approximately 15%). These data suggest that the decreases in motoneuron excitability for both the spinal cord-injured and control subjects are a result of activity-dependent changes in motoneuron properties that are independent of fatigue-related processes in the muscles.
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Affiliation(s)
- Jane E Butler
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami, Florida 33101, USA
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131
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Pitcher JB, Miles TS. Alterations in corticospinal excitability with imposed vs. voluntary fatigue in human hand muscles. J Appl Physiol (1985) 2002; 92:2131-8. [PMID: 11960966 DOI: 10.1152/japplphysiol.00835.2001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We aimed to determine whether postexercise depression of motor-evoked potentials (MEPs) could be demonstrated without voluntary muscle activation in humans. Voluntary fatigue was induced with a 2-min maximal voluntary contraction (MVC) of the first dorsal interosseous (FDI) muscle. On another occasion, "electrical fatigue" was induced with trains of shocks delivered for 2 min over the FDI motor point. Five of the twelve subjects also underwent "sequential fatigue" consisting of a 2-min MVC of FDI followed by 20 min of rest and then 2 min of motor point stimulation. Voluntary fatigue induced MEP depression that persisted for at least 20 min. Electrical fatigue induced a transient MEP facilitation that subsided 20 min after the stimulation and became depressed within 30 min. Thus MEP depression can be induced by both voluntary and electrical fatigue. With electrical fatigue, the initial depression is "masked" by transient MEP facilitation, reflecting cortical plasticity induced by the prolonged electrical stimulation. MEP depression probably reflects tonic afferent input from the exercising muscle that alters cortical excitability without altering spinal excitability.
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Affiliation(s)
- Julia B Pitcher
- Department of Physiology, Adelaide University, South Australia 5005, Australia
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132
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Kleim JA, Cooper NR, VandenBerg PM. Exercise induces angiogenesis but does not alter movement representations within rat motor cortex. Brain Res 2002; 934:1-6. [PMID: 11937064 DOI: 10.1016/s0006-8993(02)02239-4] [Citation(s) in RCA: 212] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The effects of exercise on the topography of movement representations and blood vessel density within the rat forelimb motor cortex was examined. Adult male rats were allocated to either a Voluntary eXercise (VX) or Inactive Condition (IC). VX animals were housed for 30 days with unlimited access to running wheels while IC animals were housed in standard laboratory cages. VX animals exhibited a progressive increase in the distance traveled per day and ran an average of 58.3 km across the 30-day training period. Microelectrode stimulation was used to derive high resolution maps of the forelimb representations within the motor cortex of animals from both conditions. No significant differences in the area of either distal (wrist/digit) or proximal (elbow/shoulder) movement representations were found between VX and IC animals. However, VX animals did have a significantly greater density of blood vessels within layer V of the forelimb motor cortex. These results demonstrate that increases in forelimb motor activity sufficient to induce cortical angiogenesis does not alter the topography of forelimb movement representations within forelimb motor cortex.
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Affiliation(s)
- Jeffrey A Kleim
- Department of Psychology and Neuroscience, Canadian Centre for Behavioural Neuroscience, University of Lethbridge, 4401 University Dr., Lethbridge, Alberta T1K 3M4, Canada.
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133
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Maïsetti O, Guével A, Legros P, Hogrel JY. SEMG power spectrum changes during a sustained 50% Maximum Voluntary Isometric Torque do not depend upon the prior knowledge of the exercise duration. J Electromyogr Kinesiol 2002; 12:103-9. [PMID: 11955982 DOI: 10.1016/s1050-6411(02)00010-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Endurance time (Tlim) is a relevant indicator of muscular resistance to fatigue. It has been recently shown that SEMG changes computed during shorter periods (sub-maximal durations) than the whole test duration could serve to predict Tlim. The aim of the present study was to test whether the prior knowledge of the sub-maximal duration had any influence on Tlim prediction throughout SEMG changes. For this purpose, we compared myoelectric changes estimated over a 30-s isometric contraction whose duration was known by the subjects, to those changes measured during the first 30 s of a test prolonged until exhaustion. The effort intensity was set at 50% of the maximal voluntary isometric torque (MVIT). The myoelectric manifestations of muscle fatigue appeared to change in a similar way during both sessions for temporal and spectral analyses. In conclusion, the prior knowledge of the duration of sustained isometric contraction did not influence the motor unit recruitment strategy throughout surface EMG evaluation. These results confirmed that the use of SEMG changes computed over shorter periods than expected endurance time may be applied to investigate the capability of the initial rate of SEMG changes to predict muscle endurance capacity at 50%MVIT. This may be of particular interest for patient evaluation in the clinical field.
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Affiliation(s)
- O Maïsetti
- Institut de Myologie, GH Pitié-Salpêtrière, 75651 Paris Cedex 13, France.
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