Neuromotor Mechanisms Involved in the Recovery from Local Muscular Fatigue

The phenomenon of over-recovery consists of a participant’s maximal force levels returning to values above initial levels. The present study examined the presence and causes of over-recovery following local muscular fatigue. Fourteen males completed two fatigue protocols consisting of maximal isometric dorsiflexion contractions. Upon completion of the fatigue protocol participants’ force was monitored over a 15 minute recovery period. Dorsiflexion force and surface electromyography (sEMG) from the tibialis anterior and soleus were monitored concurrently. Following the two fatigue conditions (10 and 20% force decrement) force recovered to 100.5 and 99.5% of initial levels for each condition, respectively. Surface EMG root-mean-square amplitude and MPF exhibited changes consistent with a warm-up effect. It was concluded that over-recovery was not present in the tibialis anterior following a local muscular fatigue. However, the return in force to initial values, rather than a persistent decrement as normally observed, was mediated by the warm-up effect.

Corticospinal output during muscular fatigue differs in multiple sclerosis patients compared to healthy controls

In multiple sclerosis (MS), fatigue is a common and often disabling symptom. It has multiple causes with central motor fatigue playing an important role.

Can Attention Focus Instructions Reduce the Effects of Fatigue on Balance Control?

Localized muscular fatigue has been identified to have detrimental effects on balance control, an important skill for everyday life. Manipulation of attention focus instructions has been shown to benefit performance of various motor skills including balance and has been found to facilitate endurance during fatiguing tasks. The purpose of this thesis was to determine if the use of attention focus instructions could attenuate the effects of muscular fatigue on balance control. Twenty-four participants performed a balance task (two-legged stance on an unstable platform) before and after a fatigue protocol. Trunk sway, platform excursions, and lower limb muscle activity was measured. Results suggest that use of either internal or external attention focus instructions can reduce the immediate effects of muscular fatigue of the lower limb on balance control as shown through reduced trunk sway and platform excursions. These results have relevance for individuals performing balance tasks in a fatigued state.

Análise da fadiga muscular localizada em atletas e sedentários através de parâmetros de freqüência do sinal eletromiográfico

Embora a análise no domínio da freqüência do sinal eletromiográfico (EMG) seja empregada na caracterização do processo de fadiga muscular localizada, sua aplicação, especificamente a da freqüência mediana (Fmed), é pouco explorada no âmbito esportivo. O objetivo do presente estudo foi verificar a viabilidade da aplicação do sinal EMG, através de sua análise no domínio da freqüência, como parâmetro para determinação e diferenciação no comportamento da fadiga muscular localizada. Dois grupos de sujeitos, um caracterizado como atletas (n =12) e outro como sedentários (n =12), foram submetidos a análises baseadas em procedimentos executados em três diferentes situações experimentais, todos envolvendo a modalidade de exercício isométrico: i) teste máximo para determinação da contração isométrica voluntária máxima (CIVM); ii) teste de fadiga, sustentado por 35 seg. a 80% da CIVM; iii) teste de recuperação, sustentado por 10 seg. a 80% da CIVM; neste ultimo foi monitorado o comportamento da Fmed nos três primeiros (Fmedi) e três últimos segundos (Fmedf) do sinal EMG no músculo tibial anterior durante o teste de fadiga. Durante os 10 segundos do teste de recuperação foi calculada a Fmed referente a todo o período (Fmedr). parâmetro utilizado no cálculo do índice de recuperação muscular (IRM). Os resultados apontam que a Fmedf apresentou valor menor em relação à Fmedi em ambos os grupos (p < 0,05). Quando comparado com o grupo de sedentários, o grupo de atletas apresentou valores maiores de Fmedi e Fmedf (p < 0,05). O valor médio e desvio-padrão do IRM para o grupo de atletas foram de 62,1% ± 28,7 e, para o grupo de sedentários, de 55,2% ± 27,8 (p > 0,05). Dessa forma, os resultados apresentados neste estudo permitem inferir a viabilidade na aplicação de parâmetros no domínio da freqüência do sinal EMG para a determinação e diferenciação do comportamento da fadiga muscular localizada.

Efeitos imediatos da laserterapia sobre o desempenho neuromuscular após fadiga muscular induzida: ensaio clínico controlado, randomizado e cego

The aim of this study was to investigate the immediate effects of laser therapy on neuromuscular performance in healthy subjects after a muscle fatigue. This is a clinical trial, controlled, randomized, blinded, attended by 80 volunteers of both genders, healthy, with ages between 18 to 28 years. Initially the volunteers performed an initial evaluation (EV1) using electromyography in the biceps muscle, associated with assessment in isokinetic dynamometry with 5 concentric contractions (60 °/s) for elbow flexion. The subjects were randomly allocated into 4 groups: G1 (control, n = 20), G2 (placebo, n = 20), G3 (pre-fatigue laser, n = 20), and G4 (post fatigue laser, n = 20). The muscular fatigue protocol had 30 concentric isokinetic contractions (120 °/s). We used a 808 nm laser, power of 100 mW, applied at the belly of the biceps muscle. After the speeches the volunteers performed a final evaluation (EV2). Test was applied to two-way ANOVA with post hoc Turkey, with a significance level of 5%. There was no significant difference in electromyographic evaluation. In dynamometric evaluation showed a drop in peak torque, peak torque normalized to body weight (p <0.001) and average power (p <0, 05) between the initial and final evaluations in control. Among the groups there was a significant difference between the control and the other groups in relation to peak torque (p <0.05), peak torque to body weight (p <0.001) and average power (p <0.05). Therefore, the low intensity laser therapy does not alter the immediate neuromuscular performance after fatigue

O Efeito de diferentes intervalos de recuperação entre as séries de treinamento com pesos, na força muscular em mulheres idosas treinadas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of the rest interval duration between contractions on muscle fatigue

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeitos da suplementação com L-Carnitina sobre a fadiga muscular do gastrocnêmio e a composição corporal de ratos tratados com dieta hiperlipídica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effects of Low-Level Laser Therapy on Biceps Braquialis Muscle Fatigue in Young Women

Objective: This study aims to investigate the effects of low-level laser therapy (LLLT) on biceps brachi muscular fatigue in 20 young females. Background data: Exhausting physical activity leads to muscular fatigue, which could decrease muscular strength, and may cause impairment in motor control and muscle pain. Several biochemical and biophysical resources have been studied in an attempt to accelerate the recovery of muscle fatigue. Among these, LLLT is emphasized. Methods: Twenty subjects were randomized in one laser group and one placebo group in two sessions of a crossover design experimental procedure; the second session taking place within 7 days of the first. In the first session, subjects underwent a collection of surface electromyographic (SEMG) data of the biceps brachii muscle, followed by active or placebo LLLT at the same muscle, followed then by another EMG sample of biceps brachii. Blood samples were collected five times during the experimental procedure. Second session procedures were identical to the first, with exception of LLLT, which was the opposite of the first session. The fatigue protocol consisted of 60sec of elbow flexion-extension movement performed with 75% of one maximum repetition. Blood lactate, EMG fatigue, and the number of elbow flexion-extension repetitions during the fatigue protocol were used to evaluate the effects of laser therapy (808nm wavelength, 100mW output power, power density of 35.7 W/cm(2), 70sec each point and 7J/point on eight points). Results: No statistical differences were found for eletromyographic fatigue and blood lactate values between groups. Mean numbers of elbow flexion-extension repetitions were 22.6 +/- 7.58 after placebo, and 25.1 +/- 9.89 after active LLLT group, but these differences were not statistically significant (p=0.342). Conclusions: LLLT had limited effects on delaying muscle fatigue in a young female sample, although a tendency was observed in the active laser group toward showing lower electromyography fatigue of biceps brachii muscle. No intergroup differences were found in the number of muscle contractions and lactate concentration.

Efeito da idade e de diferentes intensidades sobre o desempenho muscular de membros superiores e inferiores em mulheres

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of the rest interval duration between contractions on muscle fatigue

Background: We aimed to investigate the effect of rest interval, between successive contractions, on muscular fatigue. Methods: Eighteen subjects performed elbow flexion and extension (30 repetitions) on an isokinetic dynamometer with 80 degrees of range of motion. The flexion velocity was 120 degrees/s, while for elbow extension we used 5 different velocities (30, 75, 120, 240, 360 degrees/s), producing 5 different rest intervals (2.89, 1.28, 0.85, 0.57 and 0.54 s). Results: We observed that when the rest interval was 2.89 s there was a reduction in fatigue. On the other hand, when the rest interval was 0.54 s the fatigue was increased. Conclusions: When the resting time was lower (0.54 s) the decline of work in the flexor muscle group was higher compared with different rest interval duration.

Neural Modulation of Leg Stiffness in Response to Neuromuscular Fatigue

The spring-mass model is able to accurately represent hopping spring-like behavior (leg and joint stiffness), and leg and joint stiffness changes can reveal overall motor control responses to neural and muscular contributors of neuromuscular fatigue. By understanding leg stiffness modulation, we can determine which variables the nervous system targets to maintain motor performance and stability. The purpose of this study was to determine how neuromuscular fatigue affects hopping behavior by examining leg and joint stiffness before and after a single-leg calf raise fatiguing protocol. Post-fatigue, leg stiffness decreased for the exercised leg, but not for the non-exercised leg. Ankle and knee joint stiffness did not significantly change for either leg. This indicates that leg stiffness decreases primarily from muscular fatigue, but was not explained by ankle and knee joint stiffness. The decrease in leg stiffness may be an attempt to soften landing impact, while at the same time maintaining performance.

Muscle glycogen and blood lactate in yellowfin tuna, Thunnus albacares, and skipjack, Katsuwonus pelamis, following capture and tagging

ENGLISH: Tagging and the recovery of tagged yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas are important aspects of the investigations conducted by the Inter-American Tropical Tuna Commission in the Eastern Tropical Pacific Ocean. The results of the tagging program provide information on population structures, migrations, mortality rates and growth rates of these two species. The present experimental program was undertaken to study the relationship between muscular fatigue and high tagging mortalities in yellowfin and skipjack. SPANISH: La marcación del atún aleta amarilla (Thunnus albacares) y del barrilete (Katsuwonus pelamis), y el recobro de estos atunes marcados, son aspectos importantes de la investigación que efectúa la Comisión Interamericana del Atún Tropical en el Océano Pacífico Oriental Tropical. Los resultados del programa de marcación proporcionan información sobre la estructura de las poblaciones, migraciones, tasas de mortalidad y tasas de crecimiento de estas dos especies. El programa experimental presente fue emprendido para estudiar la relación entre la fatiga muscular y la alta mortalidad causada por la marcación en el atún aleta amarilla y el barrilete. (PDF contains 52 pages.)

Influência da fadiga no comportamento neuromuscular do quadríceps femoral, após reconstrução do ligamento cruzado anterior

Muscle fatigue is a phenomenon that promotes physiological and biomechanical disorders and their changes in healthy subjects have been widely studied and have significant importance for care in preventing injuries, but we do not have many information about its effects in patients after ACL reconstruction. Thus, this study is to analyze the effects of fatigue on neuromuscular behavior of quadriceps after ACL reconstruction. To reach this objective, participants were forty men, twenty healthy (26,90 ± 6,29 years) and twenty after ACL reconstruction (29,75 ± 7,01 years) with a graft of semitendinosus and gracilis tendons, between four to six months after surgery. At first, there was an assessment of joint position sense (JPS) at the isokinetic dynamometer at a speed of 5°/s and target angle of 45° to analyze the absolute error of JPS. Next, we applied the a muscle fatigue protocol, running 100 repetitions of isokinetic knee flexion-extension at 90°/s. Concurrently with this protocol, there was the assessment of muscle performance, as the peak torque (PT) and fatigue index, and electromyographic activity (RMS and median frequency). Finally, we repeated the assessment of JPS. The statistical analysis showed that patients after ACL reconstruction have, even under normal conditions, the amended JPS compared with healthy subjects and that after fatigue, both have disturbances in the JPS, but this alteration is significantly exacerbated in patients after ACL reconstruction. About muscle performance, we could notice that these patients have a lower PT, although there are no differences between the dynamometric and EMG fatigue index. These findings show the necessity about the cares of pacients with ACL reconstruction in respect of the risks of articulate instability and overload in ligamentar graft

Morphological aspects of neuromuscular junctions and gene expression of nicotinic acetylcholine receptors (nAChRs) in skeletal muscle of rats with heart failure

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)