Neuromuscular changes and the rapid adaptation following a bout of damaging eccentric exercise

An initial bout of eccentric exercise is known to protect against muscle damage following a repeated bout of the same exercise, however, the neuromuscular adaptions owing to this phenomenon are unknown. Aim: To determine if neuromuscular disturbances are modulated following a repeated bout of eccentric exercise. Methods: Following eccentric exercise performed with the elbow-flexors, we measured maximal voluntary force, resting twitch force, muscle soreness, creatine kinase and voluntary activation using motor point and motor cortex stimulation at baseline, immediately post and at 1, 2, 3, 4 and 7 days post-exercise on two occasions, separated by 3 weeks. Results: Significant muscle damage and fatigue was evident following the first exercise bout; maximal voluntary contraction was reduced immediately by 32% and remained depressed at 7 days post-exercise. Soreness and creatine kinase release peaked at 3 and 4 days post-exercise, respectively. Resting twitch force remained significantly reduced at 7 days (−48%) whilst voluntary activation measured with motor point and motor cortex stimulation was reduced until 2 and 3 days, respectively. A repeated bout effect was observed with attenuated soreness and creatine kinase release and a quicker recovery of maximal voluntary contraction and resting twitch force. A similar decrement in voluntary activation was observed following both bouts; however, following the repeated bout there was a significantly smaller reduction in, and a faster recovery of voluntary activation measured using motor cortical stimulation. Conclusion: Our data suggest that the repeated bout effect may be explained, partly, by a modification in motor corticospinal drive

Neuromuscular changes and the rapid adaptation following a bout of damaging eccentric exercise

An initial bout of eccentric exercise is known to protect against muscle damage following a repeated bout of the same exercise, however, the neuromuscular adaptions owing to this phenomenon are unknown. Aim: To determine if neuromuscular disturbances are modulated following a repeated bout of eccentric exercise. Methods: Following eccentric exercise performed with the elbow-flexors, we measured maximal voluntary force, resting twitch force, muscle soreness, creatine kinase and voluntary activation using motor point and motor cortex stimulation at baseline, immediately post and at 1, 2, 3, 4 and 7 days post-exercise on two occasions, separated by 3 weeks. Results: Significant muscle damage and fatigue was evident following the first exercise bout; maximal voluntary contraction was reduced immediately by 32% and remained depressed at 7 days post-exercise. Soreness and creatine kinase release peaked at 3 and 4 days post-exercise, respectively. Resting twitch force remained significantly reduced at 7 days (−48%) whilst voluntary activation measured with motor point and motor cortex stimulation was reduced until 2 and 3 days, respectively. A repeated bout effect was observed with attenuated soreness and creatine kinase release and a quicker recovery of maximal voluntary contraction and resting twitch force. A similar decrement in voluntary activation was observed following both bouts; however, following the repeated bout there was a significantly smaller reduction in, and a faster recovery of voluntary activation measured using motor cortical stimulation. Conclusion: Our data suggest that the repeated bout effect may be explained, partly, by a modification in motor corticospinal drive

Effect of omega-3 fatty acid supplementation in skeletal muscle and in the lipid profile in rats submitted to swimming

Introdução: Existe alguma evidência que sugere que os ácidos graxos ômega-3 (AGω-3) podem alterar a atividade das vias anti-catabólicas e/ou anabólicas do músculo esquelético para promover a manutenção da massa muscular. Objetivo: Analisar o efeito da suplementação de AGω-3 no músculo esquelético e no perfil lipídico em ratos submetidos à natação. Método: Sessenta ratos Wistar machos foram divididos em quatro grupos: sedentário placebo (SP), sedentário AGω-3 (Sω-3), exercício placebo (EP) e exercício AGω-3 (Eω-3). Os animais dos grupos EP e Eω-3 foram submetidos à 30 sessões de natação com duração de 45 minutos, intermitente, com sobrecarga de 15% do peso corporal, cinco dias por semana. Os animais receberam 500mg/dia de AGω-3 ou óleo de oliva (placebo) por gavagem. Após a eutanásia, amostras sanguíneas foram coletadas para dosagens de CK, DHL e lipídeos sanguíneos. Foi retirado o músculo gastrocnêmio, preparadas lâminas em HE e estimadas as áreas seccionais pelo método estereológico. Resultados: O grupo placebo submetido ao exercício (EP) apresentou menor ganho de peso comparado ao grupo sedentário placebo (SP) (p<0,0001). O grupo Sω-3 apresentou menor área das fibras musculares (p=0,018), menor valor de CK (p=0,001) e de colesterol (p<0,0001) comparado ao grupo SP. O grupo Eω-3 apresentou menor valor de DHL (p=0,029), menor valor de LDL (p=0,0002) e maior valor de HDL (p=0,035) comparado ao grupo EP. Conclusão: A suplementação com AGω-3 em ratos diminuiu a área seccional do músculo esquelético, diminuiu os níveis séricos das enzimas CK e DHL e melhorou o perfil lipídicoIntroduction: There is some evidence suggesting that omega-3 fatty acids (AGω-3) can alter the activity of anti-catabolic and/or anabolic pathways of the skeletal muscle to promote the maintenance of muscle mass. Objective: To analyze the effect of AGω-3 supplementation in skeletal muscle and in the lipid profile in rats submitted to swimming. Method: Sixty male Wistar rats were divided into four groups: sedentary placebo (SP), sedentary AGω- 3 (Sω-3), exercise placebo (EP) and AGω-3 exercise (Eω-3). The animals in the EP and Eω-3 groups were subjected to 30 swimming sessions with a duration of 45 minutes, with intermittent exercise and an overload of 15% of body weight, five days a week. The animals received 500mg/day of AGω-3 or olive oil (placebo) by gavage. After euthanasia, blood samples were collected for CK, LDH and blood lipids dosages. The gastrocnemius muscles were removed and slides were prepared with HE and an estimated cross-sectional area was calculated by the stereological method. Results: The placebo group submitted to exercise (EP) had less weight gain compared to the sedentary groups (SP) (p <0.0001). The group Sω-3 presented with a lower area of muscle fibers (p = 0,018), lower CK (p=0,001) and cholesterol (p<0,0001) compared to the groups SP. The Eω- 3 group presented lower LDH (p=0,029), lower LDL (p=0,0002) and higher value of HDL (p=0,035) compared to the EP group. Conclusion: The supplementation with omega-3 in rats submitted to swimming decreased the sectional area of the skeletal muscle, decreased CK and DHL enzyme and improved lipid profile.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Neuromuscular fatigue and endocrine responses in elite Australian Rules football players

The first purpose of this research was to establish the reliability of numerous measures obtained from a single and short duration repeated countermovement jump (CMJ) utilising a portable forceplate (Experimental Studies 1 and 2). Secondly, the response of reliable CMJ variables and T, C and T:C to a single elite level ARF match was assessed to identify the pattern of response and highlight those measures with the greatest potential for usefulness as monitoring tools across longer periods (Experimental Study 3). Finally, those variables identified as most valuable in Experimental Study 3 in addition to T, C and T:C; were measured throughout a season of elite ARF competition in order to examine the manner of their response and assess the magnitude of change in these variables in relation to performance and training and competition loads (Experimental Study 4)

Die Auswirkungen einer 90tägigen Liegephase auf Rückenschmerzen und die Bewegungsaktivität der Rückenmuskulatur

Einleitung: Die Ursache der in Schwerelosigkeit und in Liegestudien häufig auftretenden Rückenschmerzen ist bis heute noch weitgehend unklar. Gegenstand dieser Arbeit ist die Validierung eines Mobilisationsprogramms zur Linderung bzw. Verhinderung von Rückenschmerzen, wie sie im Rahmen von Schwerelosigkeit oder simulierter Schwerelosigkeit bei Bettliegestudien auftreten. Methode: Die Teilstudie ''Backpain'' war integriert in die ''Long-term-bed-rest-study'' 2001-2002. Die Untersuchungen des Projektes fanden im Rahmen von zwei 90tägigen Bettliegephasen in der Weltraumklinik MEDES-IMPS in Toulouse statt. Die Grundidee basierte auf einer 6°-Kopftieflage der Probanden, um die vaskulären und kardialen Bedingungen unter Schwerelosigkeit zu simulieren. Die Teilnehmer der Studie (n=25) wurden randomisiert einer von 3 Gruppen zugeteilt. Die Trainingsgruppe (n=9) trainierte während der Bettliegephase 3mal pro Woche die untere Extremität an einer speziell entwickelten Beinpresse. Die Kontrollgruppe (n=9) wurde während der Bettliegephase keinem Aktivitätsprogramm unterzogen. Die Mobilisationsgruppe (n=7) führte das präventive Rückenmobilisationsprogramm durch. Das zu validierende Bewegungsprogramm bestand aus langsamen Rückenbewegungen in allen drei Ebenen mit großen Amplituden und wurde fünfmal täglich durchgeführt. Darüber hinaus wurde bei allen Studienteilnehmern an insgesamt zwölf Tagen (vor, während und nach der Liegephase) die Wirbelsäulengeometrie des Rückens mittels Ultraschall sowie die elektromyographische Aktivität der wirbelsäulennahen Muskulatur erfasst. Neben der Erfassung der physiologischen Parameter wurden die Teilnehmer mittels eines standardisierten Fragebogens hinsichtlich ihrer Rückenschmerz-symptomatik befragt. Ergebnisse: Bei nahezu allen Teilnehmern traten Rückenschmerzen auf. Sie wurden fast ausschließlich im lumbalen Abschnitt deutlich rechts und links versetzt der Wirbelsäule lokalisiert und als dumpf beschrieben. Die Schmerzen waren mit reduzierten Bewegungsamplituden im lumbalen Bewegungssegment sowie einer vergrößerten thorakalen und tendenziell verkleinerten lumbalen Wirbelsäulenlänge verbunden. Die größten Schmerzen traten zu Beginn der Liegephase auf. Die Probanden der Kontroll- und Mobilisationsgruppe waren ab dem achten Tag der Liegephase schmerzfrei. Dies galt nicht für die Teilnehmer der Krafttrainingsgruppe, die während der gesamten Liegephase ein besonderes und zeitlich vom Training abhängiges Schmerzmuster zeigten. Des Weiteren traten bei den Probanden der Kontroll- und Krafttrainingsgruppe wiederum direkt am ersten Tag nach Ende der 90tägigen Liegephase verstärkt Schmerzen auf. Die Probanden der Mobilisationsgruppe waren hingegen nahezu schmerzfrei. Der Unterschied zu den beiden anderen Gruppen war signifikant. Die elektromyographischen Langzeitaufnahmen der wirbelsäulennahen Rückenmuskulatur konnten nicht belegen, dass der Schmerz durch eine aktive Tonuserhöhung der Muskulatur zustande kam. Schlussfolgerung: Das gewählte Mobilisationsprogramm des Rückens konnte den Schmerz während der ersten Liegetage nicht mindern. Dafür verhinderte es signifikant das Auftreten von Rückenschmerzen nach der Liegephase und verbesserte die Flexibilität der Probanden. Die im Rahmen der Studie gewonnenen Ergebnisse bestätigen die Erkenntnis, dass Minderbelastung und Bewegungsreduktion an der Schmerzentwicklung beteiligt sind. Des Weiteren wird aufgezeigt, dass ein dosiertes und funktionelles Bewegungsprogramm eine wirksame und kostengünstige Präventionsmaßnahme für die Schmerzentstehung nach längerem Bettaufenthalt darstellen kann. Schlüsselwörter: Bettliegestudie, EMG, Immobilisation, Mobilisationsprogramm, Rückenschmerzen, Rückenschmerz-prävention, Schwerelosigkeit, Wirbelsäule, Wirbelsäulenlänge Introduction: Until today it has to a large extent not been possible to detect the cause of back pain, particularly arising during situations of weightlessness and bed rest. The purpose of the present study is the validation of a mobilisation programme used to reduce or even prevent the occurrence of back pain, as it occures during weightlessness or simulated weightlessness such as bed rest studies. Method: The ''back pain'' study constituted a part of the ''long term bed rest study'' 2001-2002. Research was conducted at the MEDES-IMPS space clinic in Toulouse in form of two 90 day bed rest periods. Subjects were positioned in a 6° head down tilt position in order to simulate vascular and cardiac conditions of weightlessness. Participants (n=25) were randomly allocated to one of three groups. The training group (n=9) performed physical exercises with the lower part of their bodies by using a specially developed leg press, three times a week during the bed rest period. The control group (n=9) did not carry out any activities at all during the bed rest phase. The mobilisation group (n=7) completed the back mobilisation programme, as a preventive measure. Slow dorsal movements executed on all three levels in form of wide amplitudes, repeated five times each day concluded the motion programme. In addition, the dimensions of the spinal column as well as the EMG activity of the muscles adjacent to the spinal column were recorded by means of ultrasound at a total of twelve days (before, during and after bed rest). Besides measuring the physiological parameters, each participant daily filled a standardised questionnaire in order to provide information about intensity and location of back pain. Results: Almost all of the test persons demonstrated signs of back pain. Pain could exclusively be reduced to the lumbar part, the area to the left and right of the spinal column and was described as being of a dull kind. Recordings demonstrated that pain arose in conjunction with reduced motion amplitudes in the lumbar movement sector, as well as in conjunction with an increased thoracic and mostly reduced lumbar length of the spinal column. The highest amount of pain was experienced in the initial phase of bed rest. Those participants, who attended the control and mobilisation groups, evidenced a pain-free atmosphere from the eighth day of bed rest onwards. The exercise group, however, was exposed to a different kind of pain pattern during the entire phase of bed rest, which was particularly dependent from the time periods their special exercises took place. Furthermore the participants of the control and exercise groups disclosed increasing pain sensations directly on the first day after the 90 day rest period had ceased. The participants of the mobilisation group, on the other hand, experienced almost no pain at all. The difference between the other two groups proved to be significant. The EMG long-term recordings, which depicted the back musculature adjacent to the spinal column, were not able to demonstrate, however, that the pain experienced by the participants was produced by an active hypertonia of the musculature. Conclusion: The back pain, which occurred during the first days of bed rest, was not able to be reduced by the chosen mobilisation programme. Instead, it was possible to notably prevent the development of back pain after the period of rest had concluded and to improve the flexibility of the test persons.The results gained during the course of this study confirm that reduced exposure and movement contribute to the development of back pain. In addition, it accentuates the fact that a functional motion programme pro-vides an effective and measure to prevent any development of pain that may occur after longer periods of bed rest. Keywords: bed rest study, EMG, immobilisation, mobilisation programme, back pain, prevention, weightlessness, spinal column, length of the spinal colum

Effet de la douleur expérimentale tonique sur l'acquisition et la rétention d'une adaptation locomotrice

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2016-2017Introduction : Une proportion importante des individus ayant recours à des services de réadaptation physique vit avec de la douleur et des incapacités locomotrices. Plusieurs interventions proposées par les professionnels de la réadaptation afin de cibler leurs difficultés locomotrices nécessitent des apprentissages moteurs. Toutefois, très peu d’études ont évalué l’influence de la douleur sur l’apprentissage moteur et aucune n’a ciblé l’apprentissage d’une nouvelle tâche locomotrice. L’objectif de la thèse était d’évaluer l’influence de stimulations nociceptives cutanée et musculaire sur l’acquisition et la rétention d’une adaptation locomotrice. Méthodologie : Des individus en santé ont participé à des séances de laboratoire lors de deux journées consécutives. Lors de chaque séance, les participants devaient apprendre à marcher le plus normalement possible en présence d’un champ de force perturbant les mouvements de leur cheville, produit par une orthèse robotisée. La première journée permettait d’évaluer le comportement des participants lors de la phase d’acquisition de l’apprentissage. La seconde journée permettait d’évaluer leur rétention. Selon le groupe expérimental, l’apprentissage se faisait en présence d’une stimulation nociceptive cutanée, musculaire ou d’aucune stimulation (groupe contrôle). Initialement, l’application du champ de force provoquait d’importantes déviations des mouvements de la cheville (i.e. erreurs de mouvement), que les participants apprenaient graduellement à réduire en compensant activement la perturbation. L’erreur de mouvement moyenne durant la phase d’oscillation (en valeur absolue) a été quantifiée comme indicateur de performance. Une analyse plus approfondie des erreurs de mouvement et de l’activité musculaire a permis d’évaluer les stratégies motrices employées par les participants. Résultats : Les stimulations nociceptives n’ont pas affecté la performance lors de la phase d’acquisition de l’apprentissage moteur. Cependant, en présence de douleur, les erreurs de mouvement résiduelles se trouvaient plus tard dans la phase d’oscillation, suggérant l’utilisation d’une stratégie motrice moins anticipatoire que pour le groupe contrôle. Pour le groupe douleur musculaire, cette stratégie était associée à une activation précoce du muscle tibial antérieur réduite. La présence de douleur cutanée au Jour 1 interférait avec la performance des participants au Jour 2, lorsque le test de rétention était effectué en absence de douleur. Cet effet n’était pas observé lorsque la stimulation nociceptive cutanée était appliquée les deux jours, ou lorsque la douleur au Jour 1 était d’origine musculaire. Conclusion : Les résultats de cette thèse démontrent que dans certaines circonstances la douleur peut influencer de façon importante la performance lors d’un test de rétention d’une adaptation locomotrice, malgré une performance normale lors de la phase d’acquisition. Cet effet, observé uniquement avec la douleur cutanée, semble cependant plus lié au changement de contexte entre l’acquisition des habiletés motrices et le test de rétention (avec vs. sans douleur) qu’à une interférence directe avec la consolidation des habiletés motrices. Par ailleurs, malgré l’absence d’influence de la douleur sur la performance des participants lors de la phase d’acquisition de l’apprentissage, les stratégies motrices utilisées par ceux-ci étaient différentes de celles employées par le groupe contrôle.Introduction: A large proportion of individuals undergoing physical rehabilitation live with concurrent pain and locomotor disabilities. Many rehabilitation interventions targeting these locomotor disabilities are based on motor learning principles. However, very few studies have assessed the effect of pain on motor learning and none has targeted locomotor learning. The objective of this thesis was to evaluate the effect of cutaneous and muscular nociceptive stimulations on the acquisition and retention of a locomotor adaptation. Methods: Healthy individuals participated in laboratory sessions on two consecutive days. On each day, participants had to learn to walk as normally as possible while a robotized ankle-foot orthosis systematically applied a force field perturbing their ankle movements. Day 1 allowed the quantification of participants’ behaviour during the acquisition phase of motor learning. Day 2 tested retention. A cutaneous or muscular nociceptive stimulation, or no stimulation (Control group) was applied to participants during one or both learning sessions as a function of the group they were assigned to. Initially, the force field caused large deviations of participants’ ankle movements (i.e. movement errors). After walking several strides with the perturbation, participants learned to overcome it, thereby reducing movement errors. The mean absolute movement error during swing was calculated to assess participants’ performance. Detailed analysis of movement errors combined with muscle activity allowed to quantify the motor strategies employed. Results: Pain did not interfere with motor performance during the acquisition phase of motor learning. However, movement errors occurred later in the swing phase in the presence of pain, suggesting a reduction in anticipatory strategy compared to controls. For the muscle pain group, this change in strategy was associated with a reduced early activation of the Tibialis Anterior muscle. Furthermore, the presence of cutaneous pain on Day 1 interfered with participants’ performance on Day 2, when the retention test was performed in the absence of pain. However, this effect was not observed if cutaneous pain was applied on both days or if Day 1 pain was muscular. Conclusions: Results obtained showed that under particular circumstances, pain can greatly influence participants’ performance during a retention test, despite apparently normal performance during the acquisition phase of learning. This finding, observed only for cutaneous pain, appears to be more related to the change in context between the acquisition of motor skills and the retention test (pain vs no pain) than to a direct interference with the consolidation processes. Moreover, despite the fact that pain had no effect on motor performance during the acquisition phase of motor learning, motor strategies used by participants were modified when compared to controls

The Effects of Neuromuscular Fatigue on the Complexity of Isometric Torque Output in Humans

The temporal structure, or complexity, of torque output is thought to reflect the adaptability of motor control and has important implications for system function, with high values endowing greater adaptability in response to alterations in task demand. The aim of this thesis was to investigate the effect of neuromuscular fatigue on the complexity of isometric muscle torque output. It was hypothesised that neuromuscular fatigue would lead to a reduction in the complexity of muscle torque output, as measured by approximate entropy (ApEn), sample entropy (SampEn) and the detrended fluctuation analysis (DFA) ? scaling exponent. The first experimental study (Chapter 4) demonstrated that muscle torque complexity was significantly reduced during both maximal and submaximal intermittent fatiguing contractions, with the values at task failure indicative of increasingly Brownian noise (DFA ? > 1.50). It was subsequently shown in the second study (Chapter 5) that this reduction in complexity occurred exclusively during contractions performed above the critical torque. It was next demonstrated, in the third study (Chapter 6), that pre-existing fatigue significantly reduced torque complexity and time to task failure, but still resulted in consistent values of complexity at task failure regardless of the time taken to reach that point. In the fourth study (Chapter 7) caffeine ingestion was found to slow the rate of reduction in torque complexity with fatigue, seemingly through both central and peripheral mechanisms. Finally, in the fifth study (Chapter 8) eccentric exercise decreased the complexity of torque output, with values only recovering to baseline levels after 24 hours recovery, in comparison to only 10 minutes recovery following isometric exercise. These results demonstrate that torque complexity is significantly perturbed by neuromuscular fatigue. This thesis has thus provided substantial evidence that the complexity of motor control during force production becomes less complex, and that muscles become less adaptable, with neuromuscular fatigue