Introdução: Fadiga é uma manifestação clínica importante na artrite reumatoide (AR). Atualmente, a avaliação de fadiga em AR é realizada através de questionários subjetivos, incluindo aspectos emocionais e sociais. No entanto, sabe-se que a fadiga pode estar acentuada no plano periférico e esta abordagem é pouco estudada nestes pacientes. Objetivo: Avaliar a relação entre a percepção de fadiga e fadiga muscular em pacientes com artrite reumatoide. Métodos: Trinta e oito pacientes do sexo feminino com AR foram incluídos. Os pacientes foram estratificados por DAS-28 e por três grupos etários (grupo I: 32-48 anos; grupo II: 49-54 anos de idade, e grupo III: 55-65 anos de idade). A fadiga muscular [avaliado por mudanças na magnitude (root mean square-RMS) e freqüência (média de freqüência-MDF) de ativação muscular durante os 60s do teste de força de quadríceps] e percepção de fadiga (FACIT-F) foram avaliadas. Além disso, dados demográficos [duração idade e doença, calculado pelo tempo decorrido a partir de diagnóstico], hemoglobina (g/ dL), DAS-28, HAQ, qualidade de vida (SF-36) e International Physical Activity Questionnaire (IPAQ, versão longa) foram medidos. A significância foi assumida quando p≤0.05. Resultados: Nenhuma associação foi observada quando os pacientes foram estratificados por DAS-28 e quando os pacientes foram estratificados por idade no grupo III. Moderada correlações estatisticamente significativas entre MDF e FACIT-F e FACIT-TOI (r = 0,6; p = 0,03 e r = 0,5; 0,04, respectivamente) foram encontrados no grupo I. No grupo II foram encontradas moderadas correlações estatisticamente significativas entre FACIT-TOTAL e RMS e MDF (r = 0,6; p = 0,01 e r = -0,5; p = 0,04, respectivamente). Conclusão: Moderada relação entre fadiga muscular e percepção de fadiga sugere que ambas as estratégias de avaliação podem ser complementares e têm um efeito benéfico sobre comorbidades AR. / Introduction: Fatigue is a major clinical manifestation in rheumatoid arthritis (RA). Actually, the assessment of fatigue in RA is realized through to subjective questionnaires, including emotional and socials aspects. However, known to that fatigue may be sharp in peripheral plane and this approach is little studied in these patients. Objective: To assess the relationship between perception of fatigue and muscle fatigue in patients with RA. Methods: Thirty eight female patients with RA were included. Patients were stratified by DAS-28 and by three age groups (group I: 32-48 years old; group II: 49-54 years old; group III: 55-65 years old). Muscle fatigue [assessed by changes in magnitude (i.e. root mean square-RMS) and frequency (i.e. median frequency-MDF) of muscle activation during a 60-s quadriceps strength test] and perception of fatigue (FACIT-F) were assessed. In addition, demographic data [age and disease duration, calculated by elapsed time from diagnostic], hemoglobin (Hb-g/dL), DAS-28, HAQ, quality of life (SF-36) and International Physical Activity Questionnaire (IPAQ, long version) were measured. Significance was assumed when p≤0.05. Results: No association was observed when patients were stratified by DAS-28 and when patients were stratified by age in group III. Moderate statistically significant correlations between MDF and FACIT-F e FACIT-TOI (r=0.6;p=0.03 and r=0.5;0.04, respectively) were found in group I. In group II moderate statistically significant correlations were found between FACIT-TOTAL and RMS and MDF (r=0.6;p=0.01 and r=-0.5;p=0.04, respectively). Conclusion: Moderate relationship between muscle fatigue and perception of fatigue suggests that both evaluation strategies can be complementary and have a beneficial effect on RA comorbidities.

Introdução: Pacientes fibromiálgicos freqüentemente referem fadiga e estudos apontam esse sintoma como o segundo mais intenso, podendo limitar as atividades de vida diária, aumentar o estresse a até mesmo a dor. Não há um consenso se as queixas de fadiga correspondem a padrões alterados nos mecanismos de fadiga muscular, já que predominam as avaliações com questionários e escalas. O objetivo deste estudo foi avaliar a fadiga muscular em fibromiálgicos por meio da eletromiografia de superfície durante o teste de sentar e levantar. Métodos: Participaram do estudo 49 sujeitos divididos em dois grupos: Grupo Fibromiálgico (n=34) e Grupo Controle (n=15). Os padrões de fadiga muscular foram avaliados pela análise da freqüência mediana (MDF) do sinal eletromiográfico do terço distal do músculo vasto lateral durante o teste de sentar e levantar. A dor pela Escala Visual Analógica (EVA), os sintomas da fibromialgia pelo Questionário do Impacto da Fibromialgia (QIF) e o desempenho no teste de sentar e levantar pelo tempo total utilizado e número de repetições. Todos os participantes foram instruídos a realizar o teste numa velocidade confortável até a exaustão. A coleta da eletromiografia foi feita em três momentos, simultaneamente ao uso da escala de Borg para avaliação do nível de esforço percebido: início (T1), após um minuto (T2) e na exaustão (T3). Resultados: O grupo fibromiálgico apresentou MDF reduzida em T3 (p=0,04) e relato de esforço percebido mais intenso que o grupo controle em T2 (p=0,00). Foi observada correlação moderada entre MDF em T3 com as variáveis: intensidade da dor (-0,40; p=0,00) e tempo total em segundos (0,43; p=0,00). Conclusão: o grupo fibromiálgico apresentou sinais de fadiga precocemente com diminuição da freqüência mediana e percepção de esforço mais intenso comparado ao grupo controle. / Introduction: Fibromyalgia patients usually report fatigue and this symptom is the second more intense, limiting daily life activities, increasing stress and pain. There is no sense if fatigue complains are related to muscle fatigue altered patterns, since most studies performed questionnaires and scales to quantify this symptom. The aim of this study was to evaluate muscle fatigue patterns by surface electromyography during the sit to stand test. Methods: Participated 49 subjects in two groups: Fibromyalgia Group (n=34) and Control Group (n=15). Electromyography muscle fatigue patterns were evaluated by median frequency analyses (MDF) of the distal third of the vastus lateralis muscle during sit to stand test, pain by Visual Analog Scale (VAS), fibromyalgia symptoms by Fibromyalgia Impact Questionnaire (FIQ) and the test performance by total time spent in test and by number of movements. All subjects performed the sit to stand test in a comfortable velocity until exhaustion. Electromyography recording was performed in tree moments, simultaneously at Borg scale perceived effort evaluation: initial time (T1), after one minute (T2) and at exhaustion (T3). Results: Fibromyalgia group present MDF decrease at T3 (p=0,04) and more intense perceived effort at T2 (p=0,00). There was a moderate correlation for MDF in T3 with pain intensity (-0,40; p=0,00) and total time in sit to stand test in seconds (0,43; p=0,00). Conclusion: Fibromyalgia patients showed early muscle fatigue signs with MDF decrease and more intense perceived effort.

Experiments were performed to determine to what extent increments in esophageal and abdominal pressure would have on arterial blood pressure during fatiguing isometric exercise. Arterial blood pressure was measured during handgrip and leg isometric exercise performed with both a free and occluded circulation to active muscles. Handgrip contractions were exerted at 33 and 70% MVC (maximum voluntary contraction) by 4 volunteers in a sitting position and calf muscle contractions at 50 and 70% MVC with the subjects in a kneeling position. Esophageal pressure measured at the peak of inspirations did not change during either handgrip or leg contractions but peak expiratory pressures increased progressively during both handgrip and leg contractions as fatigue occurred. These increments were independent of the tensions of the isometric contractions exerted. Intra-abdominal pressures measured at the peak of either inspiration or expiration did not change during inspiration with handgrip contractions but increased during expiration. During leg exercise, intraabdominal pressures increased during both inspiration and expiration, reaching peak levels at fatigue. The arterial blood pressure also reached peak levels at fatigue, independent of circulatory occlusion and tension exerted, averaging 18.5-20 kPa (140-150 mm Hg) for both handgrip and leg contrations. While blood pressure returned to resting levels following exercise with a free circulation, it declined by only 2.7-3.8 kPa after leg and handgrip exercise, respectively, during circulatory occlusion. These results indicate that straining maneuvers contribute 3.5 to 7.8 kPa to the change in blood pressure depending on body position.

The purpose of this thesis was to improve our understanding of the progression of fatigue and recovery during repetitive work and to examine selected methods for predicting fatigue. In Chapter 2, a psychophysical methodology was used to validate the Maximum Acceptable Effort (MAE) equation of Potvin (2012) at duty cycles of greater than 0.5. The results from that study were used to evaluate the MAE equation in the higher duty cycle range. In Chapter 3, the fatigue process during complex MVC-relative force profiles was examined in a repetitive handgrip task. In Chapter 4, I examined the effect of manipulating the order of presentation of various MVC-relative force levels for a repetitive thumb flexion task. Additionally, the influence of post-activation potentiation was examined by stimulating the flexor pollicis longus (FPL) at specific time points during the complex profile. In Chapter 5, Xia and Frey Law’s (2008) three-compartment model (3CMXFL) of muscle fatigue was modified to more accurately reflect physiological processes. The model, with physiological modifications (3CMGMU), as well as the original 3CM optimized for complex tasks (3CMOPT), was optimized to predict the fatigue levels from the experiments described in Chapters 3 and 4, as well as 4 other similar experimental protocols. The predicted fatigue from the 3CMXFL was also compared to the experimental data. The 3CMOPT and 3CMGMU were compared against known endurance times. The 3CMGMU is proposed as an ergonomic tool for evaluating fatigue in repetitive tasks, and the future directions for fatigue modelling and using the MAE equation for complex force-time histories are addressed. This thesis provides the first studies of fatigue accumulation during complex MVC-relative time histories. The findings from this thesis can be applied to the workplace to reduce the risk of injury as a result of muscle fatigue. / Thesis / Doctor of Philosophy (PhD)

Low back pain (LBP) is a common occupational problem and continues to be the leading cause of occupational disability.  Among diverse known risk factors, sitting is commonly considered as an important exposure related to LBP.  Both modern living and contemporary work involve increased sedentary lifestyles, including more frequent and prolonged sitting.  At present, however, the causal role of sitting on LBP development is controversial due to the contribution of several moderating factors (e.g., task demands, duration of exposures, and presence of muscle fatigue).  A few studies have assessed low back loads in seated postures, but none has investigated the effects of prolonged sitting or time-dependent variations on spinal structure and spinal loading.  Adverse effects of muscle fatigue on low back pain are well documented, yet the specific relationship between muscle fatigue and sitting-related low back pain are not fully established.  In addition to these fundamental limitations in our understanding of the physical consequences of sitting, there is also little evidence regarding the effects of task requirements on muscle fatigue and spine loading.   Therefore, the main objectives of this work were, in the context of sitting, to: 1) develop and evaluate a method to assess paraspinal muscle fatigue using electrical stimulation; 2) develop and evaluate a method (model) to quantify biomechanical loads on the lumbar spine in a seated posture; and 3) quantify the effects of prolonged seated tasks on low back loads, body discomfort, and localized muscle fatigue (LMF).  The primary hypothesis was that exposure to sitting-related LBP risks is influenced by task requirements and sitting duration.   A muscle stimulation protocol was developed to measure stimulation responses in the lumbar extensors.  A stimulation protocol, which included one conditioning train along with three 16-second stimulation train at 2 Hz, was recommended as appropriate to measure those muscles potentially fatigued during prolonged seated tasks.  A three-dimensional, sitting-specific, fatigue-sensitive, time-dependent, electromyography (EMG)-based biomechanical model of the trunk was developed to investigate the effects of seated tasks and time-dependent variations on lumbosacral loading during sitting. Reasonable levels of correspondence were found between measured and predicted lumbosacral moments under a range of seated tasks.  Lastly, the effects of prolonged sitting and psychosocial work stress on low back were quantitatively identified.  Only prolonged sitting significantly increased trunk flexion angles and led to muscle fatigue.  Relatively weak correlations were found between subjective and objective measures, though the two fatigue measurement methods (based on EMG and stimulated responses) showed a good level of correspondence.   Overall, this work provides a quantitative assessment of biomechanical exposures associated with seated tasks.  The methods developed in this work make a contribution in terms of measurement/modeling approaches that can be used to assess LBP-relevant risks during prolonged sitting.  The results of this work provide a better understanding of the effects of prolonged sitting on the risk of developing sitting-related LBP.  Finally, results regarding the influences of prolonged sitting and psychosocial demands can be used to guide future job design. / Ph. D.

Localized muscle fatigue (LMF) is a complex, multifactorial phenomenon that involves exercise-induced decrements in the ability to generate force or power. LMF can adversely affect performance and may increase the risk of work-related musculoskeletal disorders (WMSDs), and is thus of contemporary occupational relevance. Despite considerable progress in understanding and predicting muscle fatigue, there are many uncertainties and unresolved issues that are principally associated with the physiological complexity of LMF and the diverse mechanisms that underlie LMF development. This research thus aimed to address some of the theoretical and practical issues related to muscle fatigue and recovery. Regarding the theoretical aspects, two specific muscle fatigue models (MFMs) were directly compared and some important differences in their predictions were identified. These differences were used, in part, as a basis for developing testable hypotheses and designing associated experiments. Further theoretical evaluations were conducted to explore the sensitivity of these models to the model parameters and their ability to predict endurance time in both prolonged and intermittent exertions. Sensitivity to inherent model parameters was quantified, which was relatively high in conditions involving lower to moderate levels of effort. Further assessments indicated substantial variability related to model recovery parameters, which might be related to the inability of these MFMs in simulating the recovery process. From a practical viewpoint, the effect of cycle time on the development and consequences of LMF was determined during intermittent isometric exertions. A shorter cycle time led to less fatigue development as reflected by rates of change in perceived discomfort, performance, and muscle capacity. Lastly, the dependency of muscle recovery on these different histories of fatiguing muscle contractions was explored. How a muscle recovers appeared to depend only on the state from which it starts to recover, though not the exertion history that led to that state. In summary, results of these studies may help in enhancing our understanding of fatigue and recovery processes, and in improving existing models of muscle fatigue and recovery. More accurate predictions of LMF development may help in enhancing muscle performance and in reducing the risk of musculoskeletal injuries and their associated healthcare costs. / Ph. D.

This study examined changes in task performance during performance of simulated overhead assembly task. The study objectives were to better understand the relationship between fatigue development during overhead work and task performance. This relationship is important, considering that performance changes, or decreases in task quality, have the potential for justifying and driving ergonomic changes that can help to improve worker safety. Sixteen people participated in eight experimental conditions (two levels of duty cycles, two work heights, and two hand positions). Four dependent measures based on endurance, subjective, objective, and physiological fatigue were used to quantify shoulder fatigue and were collected during the experiment. An overhead work task required participants to use a hand tool to strike targets at two reach distances above their head. Task performance was measured as a function of the closeness to the target center and the ability to apply a consistent force throughout the experiment. Data collected in this experiment is intended to provide a research basis for creating design guidelines that will help maximize efficiency and quality while reducing the likelihood of developing shoulder fatigue. / Master of Science

Repetitive stress injuries are common in the workplace where workers perform repetitive tasks continuously throughout the day. Muscle fatigue may lead to injury either directly through muscle damage or indirectly through changes in coordination, development of muscle imbalances, kinematic and muscle activation variability, and/or movement instability. To better understand the role of muscle fatigue in changes in movement parameters, we studied how muscle fatigue and muscle imbalances affected the control of movement timing, variability, and stability during a repetitive upper extremity sawing task. Since muscle fatigue leads to delayed muscle and cognitive response times, we might expect the ability to maintain movement timing would decline with muscle fatigue. We compared timing errors pre- and post-fatigue as subjects performed this repetitive sawing task synchronized with a metronome using standard techniques and a goal-equivalent manifold (GEM) approach. No differences in basic performance parameters were found. Significant decreases in the temporal correlations of the timing errors and velocities indicated that subjects made more frequent corrections to their movements post-fatigue. Muscle fatigue may lead to movement instability through a variety of mechanisms including delayed muscle response times and muscle imbalances. To measure movement stability, we must first define a state space that describes the movement. We compared a variety of different state space definitions and found that state spaces composed of angles and velocities with little redundant information provide the most consistent results. We then studied the affect of fatigue on the shoulder flexor muscles and general fatigue of the arm on movement stability. Subjects were able to maintain stability in spite of muscle fatigue, shoulder strength imbalance and decreased muscle cocontraction. Little is known about the time course for adaptations in response to fatigue. We studied the effect of muscle fatigue on movement coordination, kinematic variability and movement stability while subjects performed the same sawing task at two work heights. Increasing the height of the task caused subjects to make more adjustments to their movement patterns in response to muscle fatigue. Subjects also exhibited some increases in kinematic variability at the shoulder but no changes in movement stability. These findings suggest that people alter their kinematic patterns in response to fatigue possibly to maintain stability at the expense of increased variability. / text

Children and adolescents are thought to use oxidative metabolism to a greater extent than adults during high intensity exercise. The studies reported in this thesis examine the nature and implications of age-related differences in muscle metabolism during high intensity exercise and recovery. Chapter 4 concluded that during heavy intensity exercise, phosphocreatine (PCr) kinetics did not differ with age or sex, while Chapter 5 revealed that during very heavy intensity exercise, the fundamental τ was slower and slow component amplitude greater in men compared with adolescent boys, indicating that exercise intensity might play a role in determining age-related differences in muscle metabolism. In Chapter 6, two bouts of very heavy intensity exercise were completed, and prior exercise reduced the PCr slow component amplitude in men but not boys. Deoxyhaemoglobin (HHb) kinetics was faster in adolescents compared with adults during both heavy and very heavy intensity exercise, indicating that matching of oxygen delivery to oxygen utilisation is less precise at the onset of exercise in adolescents compared with adults. PCr recovery from high intensity exercise was faster in boys than men, but not different in girls and women, as described in Chapter 7. The speed of PCr recovery was correlated with maturity in adolescents, but was not correlated with end-exercise [PCr] or pH. Two different tests to measure mitochondrial capacity in adolescents were evaluated in Chapter 8, and a fitted curve and gated test were both used to determine PCr recovery kinetics. Finally, in Chapter 9, age-related differences in muscle metabolism and oxygenation during fatiguing exercise were examined; a strong trend for greater fatigue in adults compared with adolescents was accompanied by greater metabolic perturbation in adults. Overall, these data show that muscle metabolism and oxygenation differs between adolescents and adults during and following very high intensity exercise.

This study investigated possible effects of hypoxic training upon speed of high school sprint freestyle. Thirty-eight subjects, grouped as their two schools, performed identical loads during the ten-week program. The Experimental group used hypoxic techniques for about one-half of each workout. Pretests and posttests conducted for the 50-yard and 100-yard distances yielded highly correlated mean scores, with marked differences between the two groups. Analysis of covariance was used, selecting the .05 level for rejection. The comparison of adjusted group means indicated neither group superior at 50 yards, while the 100-yard F-ratio was significant at the .0047 level favoring hypoxic training. It is recommended that hypoxic techniques be incorporated into existing programs, possibly benefitting other strokes.