The purpose of the investigation was to determine the effect of the tonic neck posture upon fatigue induced by exhaustive exercise of the knee extensor muscles of college women. The subjects were college females enrolled in physical education activity classes at North Texas State University. The F ratio was used to determine significance of the difference in fatigue measures in the three head positions. The results of the present investigation revealed no statistically significant difference between the three head positions with respect to their influence on endurance of the leg extensors. Conclusions were that the tonic neck reflex does not facilitate or inhibit leg extensor endurance.

Introdução: A dor lombar crônica pode ser definida como dor ou desconforto persistente por mais de 12 semanas nos níveis lombar e sacral da coluna vertebral. Cerca de 5% dos pacientes apresentam comprometimento de raiz nervosa, e uma razão comum é a herniação discal. Os músculos multífido lombar (ML) e transverso do abdome (TrA) são preferencialmente acometidos frente a episódios de dor lombar. Contudo, há escassa literatura que tenha avaliado a fadiga do ML e a capacidade de ativação do TrA em indivíduos com e sem hérnia de disco lombar. Objetivo: Avaliar a fadiga do músculo multífido lombar e a capacidade de ativação do transverso do abdome em indivíduos com hérnia de disco e dor lombar crônica, e controle. Métodos: Participaram do estudo 60 indivíduos com idade entre 20 a 50 anos, divididos em dois grupos: Hérnia Lombar (GHL) com dor há mais de três meses (n=30) e Grupo Controle (GC) sem dor (n=30). A fadiga do multífido lombar foi avaliada com a eletromiografia de superfície durante a realização do teste de esforço de Sorensen e a capacidade de ativação do TrA pela Unidade de Biofeedback Pressórico (UBP). A dor foi avaliada com a escala visual analógica - EVA e questionário McGill de Dor, a incapacidade funcional pelo Índice de incapacidade de Oswestry e o relato de esforço percebido pela escala de Borg. O nível de significância adotado foi de 5%. Na análise dos dados de frequência mediana quanto menor o valor maior a fadiga. Resultados: Houve aumento da fadiga nos dois grupos, porém mais intensa no GHL (p=0,0001) proporcionando a instalação da fadiga em menor tempo (163 s). Na capacidade de ativação do TrA, o GHL apresentou ativação insuficiente (-0,9 mmHg) e GC próximo a valores ideais ( -3,9 mmHg). Na escala de Borg, houve diferença entre os grupos para o esforço inicial (p=0,0002), contudo não foi observado diferença para o esforço final (p=0,0611). O GHL apresentou dor moderada (6,4 cm) quando avaliada pela EVA e pelo Questionário McGill de dor nas categorias sensorial (19,2) afetiva (8,6) e total (36,3) e incapacidade funcional mínima. Conclusão: Os indivíduos com hérnia de disco e dor lombar crônica apresentam maior fadiga do músculo multífido lombar e ativação do transverso do abdome insuficiente quando comparados aos controles. / Introduction: Chronic low back pain can be defined as pain or discomfort lasting more than 12 weeks in the lumbar and sacral levels of the spine. About 5% of patients have nerve root impairment, and the more common etiology is the disc herniation. The lumbar multifidus (LM) and transversus abdominis (TrA) muscles are often affected in low back pain. However, the literature on the fatigue assessment of ML and the ability of TRA activation in individuals with and without lumbar disc herniation is scarce. Objective: To evaluate the lumbar multifidus muscle fatigue and transversus abdominis activation in individuals with disc herniation and chronic low back pain, and control. Methods: The study included 60 subjects aged 20 to 50 years, divided into two groups: lumbar herniated group (GLH) with pain for more than three months (n = 30) and control group (CG) without pain (n = 30). The fatigue of the lumbar multifidus was measured with surface electromyography during the Sorensen test and ability of activation of TRA with Unit Biofeedback pressure (PBU). Pain was assessed by visual analog scale - VAS and McGill pain questionnaire, functional disability by Oswestry Disability Index, and the reporting of perceived exertion with Borg scale. The significance level was established in 5%. Results: We found increased fatigue in both groups however more intense in GLH (p=0.0001) providing the onset of fatigue in less time (163 s). The ability to activate the TrA, the GLH showed insufficient activation (-0.9 mmHg) and CG near the ideal values (-3.9 mmHg). In Borg scale, difference was observed between groups for the initial effort (p = 0.0002), however no difference was observed for the final effort (p = 0.061). The GLH had moderate pain (6.4 cm) when assessed by the VAS and the McGill Pain Questionnaire in sensory (19.2), affective (8.6) and total (36.3) categories and minimal functional disability. Conclusion: Individuals with disc herniation and chronic low back pain have higher fatigue of lumbar multifidus and insufficient transversus abdominis muscle activation when compared to controls.

A fadiga muscular é um fenômeno extensivamente estudado, especialmente por sua influência sobre o desempenho físico. Diversos estudos têm demonstrado que a acidose muscular, ocasionada pelo acúmulo de íons H+ no interior da célula muscular, é um fator limitante para o desempenho físico durante exercícios físicos de alta intensidade. Assim, estratégias com o objetivo de atenuar a queda do pH intramuscular têm o potêncial de se destacar como agente tamponante. Dentre elas, a suplementação de bicarbonato de sódio tem mostrado ser uma interessante estratégia nutricional para o aumento do desempenho anaeróbio. Recentemente a suplementação de lactato tem se mostrado como um possível agente tamponante. Teoricamente a suplementação de lactato pode aumentar os níveis sanguíneos de pH e bicarbonato, assim aumentando a capacidade tamponante extracelular. Os poucos estudos sugerem um potêncial ergogênico desta estratégia nutricional, embora a falta de estudos sugere a necessidade de mais estudos que atestem a eficácia ergogênica deste suplemento. Portanto, esse estudo tem por objetivo investigar o efeito da suplementação crônica de lactato de cálcio sobre os níveis sanguíneos de pH e bicarbonato e desempenho intermitente de alta intensidade; e ainda, compará-los com a suplementação de bicarbonato de sódio. Foram recrutados 18 atletas (idade 26 ± 5 anos; massa corporal 88,8 ± 6,8 kg; estatura 1,78 ± 0,7m; gordura corporal 18,6 ± 6,2 %). A pesquisa teve um desenho randomizado, controlado por placebo, duplo-cego cross-over. Os sujeitos foram alocados em 3 tratamentos diferentes: placebo, lactato de cálcio e bicarbonato de sódio. Todos os tratamentos suplementaram a dose de 500 mg.kg-1, divididas em 4 doses diárias, por um período de cinco dias consecutivos, seguido por dois dias de washout. Os indivíduos foram submetidos a testes de desempenho físico anaeróbio para membros superiores. Foram realizadas 4 séries do teste de Wingate, com duração de 30 segundos em cada série, e carga fixa em 4% do peso corporal, separadas por períodos de recuperação ativa de 3 minutos. As variáveis de potência média, pico e trabalho total, foram usados para verificação de alterações no desempenho em virtude dos tratamentos. Foi ainda avaliado os níveis sanguíneos de pH, bicarbonato e lactato no repouso, após o esforço e 5min após o esforço. A análise de reprodutibilidade do teste de Wingate mostrou que não houve diferenças entre as duas familiarizações e o teste pré-suplementação. As variáveis sanguíneas não foram diferentes entre os testes, e evidenciaram o potêncial do teste em diminuir pH, bicarbonato e excesso ácido-base e aumentar o lactato plasmático. Os resultados mostram que a suplementação de lactato de cálcio não foi capaz de melhorar o desempenho ou influenciar variáveis sanguíneas de bicarbonato e pH, no entanto a suplementação de bicarbonato de sódio melhorou o desempenho em ~2,9% e aumentou os níveis basais de bicarbonato sanguíneo, mas não alterou o pH. Dessa forma conclui-se que tal estratégia não é capaz de aumentar a capacidade tamponante, tampouco de promover melhoras no desempenho intermitente de alta intensidade / Muscle fatigue is an extensively studied phenomenon, especially due to its relevance to performance. Several studies have shown that muscle acidosis caused by hydrogen ion (H+) accumulation in the muscle cell is a limiting factor to physical performance during high-intensity exercise. Thus, strategies aimed at attenuating the fall in intramuscular pH during exercise have the potential to improve performance. Among these strategies, sodium bicarbonate supplementation has been shown to be an effective nutritional strategy for increasing anaerobic performance. Recently, lactate supplementation has been suggested to be an equally effective buffering aid. Theoretically, lactate supplementation can increase blood pH and bicarbonate levels, thereby increasing extracellular buffering capacity. The few studies available to date have shown the ergogenic potential of this nutritional strategy, although the lack of studies with chronic supplementation in addition to the lack of reliable physical tests suggests the need for more studies to confirm the efficacy of lactate supplementation. Therefore, this study aimed to investigate the effect of chronic calcium lactate and sodium bicarbonate supplementation on blood pH, bicarbonate and high-intensity intermittent exercise performance. Eighteen athletes (age 26±5 years; body mass 88,8±6,8 kg; height 1,78± 0,7m; body fat 18,6±6,2 %) were recruited to this randomised, double-blind, placebo-controlled, crossover and counterbalanced study. The participants\' underwent 3 different treatments: placebo, calcium lactate and sodium bicarbonate. The dose in all conditions was 500 mg·kg-1, divided into 4 daily doses, for 5 consecutive days, followed by a 2-day washout period. On the fifth day of supplementation, individuals underwent 4 bouts of the Wingate upper-body anaerobic test. The bouts lasted 30 seconds, with a fixed load of 4% body mass and were separated by active recovery periods of 3 minutes. Mean and peak power, as well as total work done, were recorded during each bout. In addition, blood pH, bicarbonate and lactate were determined at rest, immediately after exercise and 5 min after exercise. The Wingate test reproducibility analysis showed no differences between both familiarisations and a pre-supplementation test while blood variables were not different between tests. Post-exercise values highlighted the potential of the test to decrease blood pH, bicarbonate and base excess and to increase plasma lactate. Results showed that calcium lactate supplementation did not improve upper-body Wingate performance, likely due to a lack of change in blood bicarbonate and pH prior to exercise. Sodium bicarbonate supplementation improved performance by ~2.9% following increased pre-exercise levels of blood bicarbonate but not pH. It can be concluded that calcium lactate supplementation is not capable of increasing buffering capacity, and thus does not promote improvements in high-intensity intermittent performance

by Jing Xian Li. / Thesis (Ph.D.)--Chinese university of Hong Kong, 1998. / Includes bibliographical references (p. 137-151). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Made available in DSpace on 2014-06-11T19:30:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-05-10Bitstream added on 2014-06-13T20:40:44Z : No. of bitstreams: 1 fraga_chw_dr_rcla.pdf: 2287250 bytes, checksum: 19a31b7d57d53f1dce9bd848d8b99deb (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O presente estudo teve como objetivos: (1) determinar e comparar os Limiares de Fadiga Eletromiográficos (EMGLF) de diferentes músculos com limiares metabólicos, durante protocolo de corrida incremental; (2) comparar o sinal eletromiográfico (EMG), a freqüência de passada (FP) e amplitude de passada (AP) entre três intensidades de exercício, correspondentes a 60%, 80% e 100% da velocidade máxima (Vmáx); (3) analisar o efeito de um protocolo incremental de corrida sobre o comportamento do sinal EMG obtido a partir de contrações isométricas e dinâmicas. Para cada objetivo proposto, será apresentado um artigo, nos quais foram avaliados indivíduos com diferentes experiências na modalidade: corredores recreacionais (CR), sem treinamento específico em corrida; e, corredores (CO) que treinavam para competições específicas da modalidade. Os protocolos de corrida foram realizados com velocidades iniciais de 8 km.h-1 para CR e de 10 km.h-1 para CO, com incrementos de 1 km.h-1 a cada três minutos até a exaustão. Esses protocolos diferiram de acordo com o intervalo entre cada estágio incremental: 30 segundos (protocolo A) e 120 segundos (protocolo B). Nos dois protocolos, foram coletados, nos intervalos, amostras de 25 μl de sangue para determinação dos limiares metabólicos. Apenas no protocolo B, foram coletados sinais EMG de contrações isométricas submáximas nos intervalos entre os estágios incrementais. Sinais eletromiográficos (EMG) foram registrados por meio de eletrodos de superfície bipolares posicionados sobre os músculos iliocostal lombar (IC), reto femoral (RF), vasto lateral (VL), vasto medial (VM), bíceps femoral (porção longa) (BF), tibial anterior (TA), e gastrocnêmio (porção lateral) (GL). Os principais resultados encontrados apontam que (1) o EMGLF mostrou-se similar entre os diferentes músculos analisados e entre a velocidade correspondente... / This study aimed to: (1) determine and compare the electromyographic fatigue threshold (EMGFT) of different muscles with metabolic thresholds during incremental running protocol, (2) compare the electromyographic signal (EMG), the stride frequency (SF) and the stride length (SL) in three exercise intensities corresponding to 60%, 80% and 100% of maximum velocity (Vmax), (3) analyze the influence of an incremental running protocol on the behavior of the EMG signal obtained from isometric and dynamic contractions. An article will be presented for each proposed aim. The subjects were divided according to their experiences in the sport in: Recreational Runners (RR), with no specific training in running, and Runners (RU) who trained specifically for running competitions. The running protocols were performed with initial speeds of 8 km.h-1 for RR and 10 km.h-1 for RU. The increments were of 1 km.h-1 in every three minutes until exhaustion. The two protocols used differed in their interval between each increments in: 30 seconds (protocol A) and 120 seconds (protocol B). In both protocols, blood samples of 25 μl were collected at the intervals between increments to determination the metabolic thresholds. Only in the protocol B, EMG signals were collected from submaximal isometric contractions in the intervals between incremental stages. Electromyographic signals (EMG) were recorded by bipolar surface electrodes placed over the lumbar iliocostal (IC), rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris (long portion) (BF), tibialis anterior (TA) and gastrocnemius (lateral portion) (GL). The main findings indicate that (1) EMGFT proved to be similar among the different muscles and between the speed at which the anaerobic threshold occurred. Therefore, the EMGFT allowed the estimation of the transition from aerobic to anaerobic metabolism noninvasively in the two... (Complete abstract click electronic access below)

Paralyzed muscle fatigues more quickly than intact muscle. The reason for this difference is currently unknown. This work will bridge this gap in knowledge by evaluating the predictive abilities of higher-resolution closed-form mathematical models of muscle force and fatigue. Knowledge garnered from this effort will suggest possible mechanisms for the differences in fatiguability of muscle in different states of health. The hypothesis to be tested is that the concept missing from present models, and thus the present understanding of the physiology, is the dynamic behavior of divalent calcium (Ca2+) during induced muscle contraction. If the behavior of Ca2+ can be understood as a Riccati-Bass diffusion process, muscle force and low-frequency fatigue in paralyzed muscle can be more accurately predicted over the time course of response to neuromuscular electrical stimulation. The abilities of existing mathematical models to predict force and low-frequency fatigue are compared to the predictive abilities of new models that include the Riccati-Bass equation. There are several major findings of this study. First, it was found that the structure of the Conaway models better predicts force and low-frequency fatigue than do the Ding models. Second, the cross-bridge friction is the most influential factor in generating force in fresh muscle at frequencies greater than 5 pps. Finally, the calcium leak current is most influential in low-frequency fatigue in paralyzed muscle. It is concluded that the process of muscle fatigue occurs as calcium channel remodeling and inactivation of excitation-contraction coupling from ionic crowding accelerate with every additional contraction.

Muscle fatigue is ubiquitous in every day life.Muscle fatigue might be considered as an altered state of motor behaviour, which impairs motor performance. By contrast, muscle fatigue could also be considered a positive phenomenon, which protects muscle tissue from damage that might be incurred to it by overuse. The principal aim of the thesis was to explore some of the mechanisms of muscle fatigue at the spinal level in animal models.The activation of multiple motor units of a single calf muscle may influence contractile properties of its neighbouring, otherwise inactive units, providing evidence for spatial spreading of fatigue between different muscle parts. The release of metabolites, their action on inactive muscle units and the effects of local hypoxia are the most likely causes. Fatigue-induced metabolite shift in the interstitium provokes excitation and/or sensitisation of high-threshold afferent fibers, with complex effects on the spinal premotoneuronal network involved in the modulation of motoneuronal output. This was examined by studing the intrasegmental lamellar distribution of the lumbar spinal interneurons following fatiguing contractions of the triceps surae muscle. Furthermore, fatigue of calf muscles enhanced the activity of fusimotor neurons to these muscles irrespective of the regime of muscle activity (isometric vs. lengthening) in conditions that simulate locomotion. Altered fusimotor activity, through increased or maintained muscle spindle afferent responsiveness may be advantageous, providing support to the skeletomotor activity and enhanced information about muscle periphery to higher nervous centres. The particular effects of interneuronal network at motor input (presynaptic inhibition system) and output (recurrent inhibition system) stages were then addressed. Fatigue of triceps surae muscle induced a suppression of the monosynaptic reflex. The intensity of presynaptic inhibition increased, while the intensity of recurrent inhibition decreased. Post fatigue-evoked changes in monosynaptic reflexes and presynaptic inhibition indicate the possibility that high-threshold afferents inhibit group Ia terminals pre-synaptically, which would allow fatigue-induced signals from the muscle to reduce the relevance of proprioceptive feedback. Besides intrasegmental, intersegmental spreading of nociceptive signals was explored. Activation of sensory afferents from dorsal neck muscles by capsaicin induces powerful activation of interneurons located in the cervical spinal cord, as well as a widespread activation of cells in lumbar spinal cord segments. The results confirm the pivotal role of small diameter muscle afferents in the orchestration of segmental responses to fatigue and show complex interactions that may lead to limited accuracy of motor output. They also depict processes that may be related to, and even become precursors of chronic muscle pain.

A traditional warm-up (WU) for track sprinters usually includes a general WU, a series of mobility drills and some short sprint strides lasting 30-60 min in total. A WU of this duration might cause significant fatigue and impair sprint performance. Aim: To test the hypothesis that a traditional high intense warm-up of long duration would elicit fatigue and impair sprint performance. Methods: Five highly trained males competitive in endurance sports performed three different WU protocols on separate days in their postseason period. Their mean ± SD age, body mass and height were 24.2 ± 1.6 years, 78.4 ± 7.8 kg, 179.6 ± 8.8 cm. The study participants performed a timed 60 meter sprint on an indoor track. The traditional warm-up (LONG), started with 10 min of easy running; then 7 min of mobility drills followed by five sprints performed with 3-min break in between. The total duration of LONG was 35 minutes. The experimental warm-up (SHORT) was shorter and less intense; 10 min of easy running was followed by just one sprint. Both warm-up protocols were followed by 10 min of recovery, where participants were not allowed to sit down. A third test occasion served as control (CON), where participants did not conduct physical activity prior to the time trial, only 10 min of recovery. Participants also rated the satisfaction of their performance on a 10 point scale. Results: The results of 60 m time trial performance showed no significant differences among the different WU protocols (P = 0.20). The 60 m performance was better for SHORT (8.02 ± 0.10 sec) than for LONG (8.08 ± 0.16 sec) and CON (8.20 ± 0.21 sec). 4 of 5 participants experienced their fastest time trial following SHORT. It appeared that participants were significantly faster following SHORT (7.99 ± 0.22 ms-1) compared to LONG (7.77 ± 0.33 ms-1) in the final 10 m of the time trial (P = 0.05). The satisfaction after SHORT scored highest (6.9), followed by LONG (5.9) and CON (4.5). Conclusions: There is no significant difference between a traditional WU compared to a WU of shorter duration and lower intensity. The traditional WU showed a significant decline in running speed in the final stage of the time trial, which might be caused by fatigue.

Background: Extensive literature has described a decrease in force output performance in the local muscle groups after static stretching, and static stretching has therefore been recommended not to be performed during warm-ups. A recent study showed evidence of a cross-over effect in regard to static stretching, i.e. non-local muscles were also affected by static stretching. This result could however be due to fatigue in the muscle groups stretched, and a fatigued condition has previously shown cross-over effects in several studies. Aim: The aim of the study was to (1) examine if upper-limb static stretching and muscle fatigue display a cross-over effect that show changes in force output in the lower limbs, and (2) if there was a difference between the effects of the static stretch protocol and the muscle fatigue protocol for the purpose of examining if fatigue is the larger factor for cross-over. Methods: Concentric maximal jump height of 15 subjects with previous strength training experience of at least one year was measured and the subjects subsequently performed both intervention protocols in a random order. After each protocol concentric jump height was measured again. The static stretch protocol consisted of a static stretch for the shoulder at an intensity of “Very hard”, 10 repetitions of 30 second stretches with 15 seconds rest in between repetitions. The muscle fatigue protocol consisted of 10 repetitions of 30 seconds isometric muscle contraction in the same position with 15 seconds rest between repetitions at an intensity of “Very hard”. The data was collected on an infra-red contact mat and differences between the mean jump heights pre- and post each protocol and between the different protocols were analyzed with pair sample t-test.   Result: Mean concentric jump height (± standard deviation, SD) was 25.31 (±9.4) cm for the baseline jumps, 23.66 (±8.89) cm post static stretch intervention jumps and 24.13 (±8.90) cm post muscle fatigue intervention jumps. This indicates a cross-over effect on force output in the legs post static stretching with a mean reduction of 1.65 cm (p=0.001). Upper-limb muscle fatigue indicated a cross-over effect on force output in the legs with a mean reduction of 1.18 cm (p=0.032). There was no statistical significance between the two protocols (p=0.146). Conclusion: The results presented a cross-over effect on both conditions. This is in line with previous research in the area. The results implicate that static stretching and muscle fatigue effects the central nervous system, which can lead to impairments in performance in non-local muscles. This can be considered in warm-up and exercise program design when force output is of great importance for performance

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 5 uppsatser.