Work-related musculoskeletal disorders (WMSDs) are prevalent in the workplace, and epidemiology studies show that these problems do not tend to diminish. While the use of new and advanced technology has substantially reduced the amount of physical workload, repetitive manual activities are still typically observed in various work settings. Despite their fairly low workload intensity, prolonged repetitive tasks have been associated with the development of musculoskeletal complaints and problems. Research on localized muscle fatigue (LMF) has been viewed as a viable endeavor toward understanding the processes and mechanisms associated with WMSDs. A mounting of evidence on local fatigue during sustained static work has been presented, but much less is known with respect to muscle fatigue during more complex activities. A study was conducted with the primary objectives of determining the repeatability of several commonly used fatigue measures, and to evaluate the presence of long-lasting effects of fatigue from different recovery periods. Based on low-level intermittent arm abductions, findings from this study demonstrated that the use of perceptions of muscular discomfort and muscle strength as fatigue measures was satisfactory. In contrast, electromyography (EMG)-based measures were characterized by a fairly low repeatability. The study also suggested that, whenever practical, two days of recovery should be allotted in studies involving multiple exposures to fatiguing protocols. Long lasting effects of fatigue could be present when shorter amounts of recovery period were assigned. A second study was also carried out to investigate the effects of work parameters (force-level, work-rest ratio, and work cycle) on muscular fatigue during intermittent static efforts. It was suggested that work conditions with muscular contraction level less than 12% MVE was non-fatiguing, irrespective of the values of the work parameters selected. Intermittent work with higher levels of muscle contraction might be acceptable, but it was dependent upon interactions of the other two parameters. The effects of dynamic work conditions on muscle fatigue were investigated in another study. Findings from this third study suggested that muscles responded differently under dynamic conditions and the use of typical EMG measures (dynamic EMG) could be less sensitive. This study further demonstrated that fatigue evaluations during such conditions were difficult, and only a limited number of EMG-based measures could be potentially employed. / Ph. D.

The purpose of this study was to establish an exercise protocol that demonstrated a relationship between rest-interval duration and the exercise induced human growth hormone (hGH) response. Ten recreationally trained male subjects (23 ± 0.9 yrs) performed three leg extension trials on an Eagle — Cybex leg extension machine that consisted of 4 sets of 10 repetitions. The workload and volume was kept constant, but each trial had different rest-interval durations. Rest-interval durations between sets were at: 30 sec intervals (T-30), 60 sec intervals (T-60), or 120 sec intervals (T-120). Blood samples were obtained pre- and 0 — 30 minutes post-exercise and analyzed for lactate and hGH. All blood lactates rose significantly above baseline after exercise, with no differences in time of occurrence between trials. Blood lactates were significantly greater after the T-30 trials, compared to that of the T-60 and T-120 trials. There was no significant difference in hGH concentrations between trials. However, the data did suggest a relationship between rest-interval duration and the variability of hGH responses. The T-30 trials yielded significantly greater variation in hGH concentrations than the T-120 trials, and the T-120 trials showed significantly less variation than both the T-30 and T-60 trials. Although significant differences were found in these variations between trials, they did not prevent any significant differences in concentrations between trials from being found. In summary, the results of this study demonstrated an exercise related increase in lactic acid that had an inverse relationship to the length of the rest-intervals. hGH data on the other hand, did not show a relationship between rest-interval duration and the hGH concentrations. The connection between rest-interval duration and variability of hGH responses could possibly suggest that hGH values may have been significantly different if an exercise protocol higher in volume were utilized. Additionally, the results indicate that there is no direct relationship between blood lactate and hGH concentrations, as others have suggested. / School of Physical Education, Sport, and Exercise Science

Fibrinolysis is the process by which fibrin blood clots are dissolved. Fibrinolytic research is clinically relevant because decreased fibrinolytic potential is linked to increased risk of an ischemic event. Fibrinolysis is known to increase in response to aerobic exercise, however, few research studies have focused on the fibrinolytic response to resistance exercise. Furthermore, women are severely underrepresented in fibrinolytic research, and there are no current studies that focus on women and resistance exercise. Estrogen has been shown to affect basal fibrinolytic potential resulting in the need for fibrinolytic research focused on female subjects. Body composition is known to influence basal fibrinolysis leaving individuals with higher absolute amounts of body fat at risk for cardiovascular events due to decreased fibrinolytic potential. Little is known, however, about the influence of body composition on the fibrinolytic response to exercise. Purpose. The purpose of this study was to describe the fibrinolytic response to acute resistance training in young women, and further, to determine how body fat percentage affects fibrinolysis at rest and following resistance exercise. Methods. Twenty-three sedentary, healthy women (22.5 ± 4 yrs, 22.3 ± 3.0 kg•m 2) participated in the study. Body fat percentage and fat distribution were assessed using dual-energy X-ray absorptiometry (DEXA), and subjects were separated into two groups by body fat percentage: <30% (lean, n=12) and >30% (obese, n=11). Each subject performed 6 sets of 10 leg extension repetitions at an intensity associated with 70% of her one-repetition maximum. The two primary mediators of fibrinolytic potential, tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1(PAI-1), were assessed at baseline and immediately after exercise in venous blood. Results. tPA activity increased in response to acute resistance exercise (p<0.05), however, there was no significant change in PAI-1 activity (p>0.05). A significant main effect of group was observed, indicating the lean women had higher tPA activity (p<0.05) and lower PAI-1 activity (p<0.05) than the obese group. A significant time x group interaction indicated that the tPA response was blunted in the obese group (p<0.05). Conclusions. Fibrinolytic potential increases in response to acute resistance exercise in young women due to increases in tPA activity. Obese women demonstrate a decreased fibrinolytic potential at rest and following acute resistance exercise compared to lean women. Given the relationship between fibrinolytic potential and outcomes of cardiovascular disease, these physiological responses suggest that overweight women may be at elevated risk of an adverse cardiovascular event both at rest and during exercise. / School of Physical Education, Sport, and Exercise Science

Title: Effect of two active recovery methods on repeated bout of finger flexors isometric performance. Goals: Compare two methods of active recovery - global and local, during repeated isometric performance and learn the difference between active and passive recovery. Method: Ten recreational athletes in average age 30,4 ± 5,9 years performed in a random cross-over desing 3 sessions with 3 repeated isometric intermittent contraction. The effect of active global recovery, active local recovery and passive recovery between repetions was monitored. Results: More effective type of recovery was active recovery. There was no difference between both active recovery methods. Performed decrease in active global recovery was activleast effective method of recovery was passive recovery. Decrease in the time in active global recovery was 21,7s (29,77%) and in active local recovery 20,8s (30,1%). The least effective was passive recovery. There was decrease 24,6s (35,34%). Key words: recovery, active recovery, local recovery, finger flexors, interrmitent, isometric contraction.

by Choi Man. / Year shown on spine: 1997. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 146-153). / Abstract --- p.1 / Chapter 1 --- Introduction --- p.3 / Chapter 1.1 --- Anatomy --- p.4 / Chapter 1.2 --- Kinematics of the overhead sports --- p.6 / Chapter 1.3 --- Isokinetics assessment of the shoulder rotators --- p.8 / Chapter 1.4 --- Objectives of the study --- p.10 / Chapter 1.5 --- Method of investigation --- p.11 / Chapter 1.5.1 --- Subject --- p.12 / Chapter 1.5.2 --- Equipment --- p.13 / Chapter 1.5.3 --- Protocol --- p.14 / Chapter 1.6 --- Data Management --- p.17 / Chapter 1.7 --- Clinical application --- p.18 / Chapter 1.8 --- Definition of terms --- p.18 / Chapter 2 --- Literture Review --- p.20 / Chapter 2.1 --- Anatomy --- p.20 / Chapter 2.1.1 --- Ligament --- p.21 / Chapter 2.1.2 --- Muscles --- p.24 / Chapter 2.2 --- Biomechanics of the overhead movement --- p.30 / Chapter 2.2.1 --- Wind up Phase --- p.32 / Chapter 2.2.2 --- Cocking Phase --- p.33 / Chapter 2.2.3 --- Acceleration Phase --- p.36 / Chapter 2.2.4 --- Deceleration Phase --- p.38 / Chapter 2.3 --- Eccentric contraction --- p.40 / Chapter 2.3.1 --- Physiology of eccentric contraction --- p.40 / Chapter 2.3.2 --- Mechanical trauma in eccentric contraction & DOMS --- p.41 / Chapter 2.3.3 --- Eccentric contraction in Plyometric --- p.43 / Chapter 2.3.4 --- Role of eccentric contraction in overhead sports --- p.44 / Chapter 2.3.5 --- Comparison with concentric contraction --- p.45 / Chapter 2.4 --- Isokinetics --- p.46 / Chapter 2.4.1 --- Introduction to isokinetics --- p.46 / Chapter 2.4.2 --- Reliability of isokinetic assessment on Shoulder rotator --- p.48 / Chapter 2.4.3 --- Agonist / Antagonist Ratio --- p.51 / Chapter 2.4.4 --- Variation of torques with testing protocols --- p.52 / Chapter 2.4.5 --- Comparison of muscle torques in different groups --- p.56 / Chapter 2.4.6 --- Isokinetic eccentric contraction of shoulder Rotators --- p.62 / Chapter 3 --- Method of Investigation --- p.63 / Chapter 3.1 --- Subject --- p.64 / Chapter 3.1.1 --- Part One --- p.64 / Chapter 3.1.2 --- Part Two --- p.65 / Chapter 3.1.3 --- Criteria of subject recruitment --- p.65 / Chapter 3.2 --- Equipment --- p.66 / Chapter 3.2.1 --- Collection of medical history and general informations --- p.66 / Chapter 3.2.2 --- Test for general laxity --- p.66 / Chapter 3.2.3 --- Test for shoulder impingement --- p.72 / Chapter 3.2.4 --- Test for shoulder instability --- p.73 / Chapter 3.2.5 --- Joint range measurement --- p.76 / Chapter 3.2.6 --- Isokinetic strength of shoulder rotators --- p.78 / Chapter 3.3 --- Calibration --- p.79 / Chapter 3.4 --- Testing procedure --- p.79 / Chapter 3.4.1 --- "Explanation,warning & consent" --- p.79 / Chapter 3.4.2 --- Warming up --- p.80 / Chapter 3.4.3 --- Screening --- p.81 / Chapter 3.4.4 --- Isokinetic testing of the rotational strength of both shoulders --- p.81 / Chapter 3.5 --- Operator --- p.87 / Chapter 3.6 --- Data Management --- p.88 / Chapter 3.6.1 --- Part One --- p.88 / Chapter 3.6.2 --- Part Two --- p.89 / Chapter 4 --- Result --- p.91 / Chapter 4.1 --- Part One --- p.89 / Chapter 4.1.1 --- Intra-class correlation coefficient --- p.90 / Chapter 4.1.2 --- Correlation between the PTR & the ASMSTR --- p.92 / Chapter 4.2 --- Part Two --- p.94 / Chapter 4.2.1 --- Comparison between the Members in the Hong Kong Badminton Team with the Non-athlete Subjects --- p.94 / Chapter 4.2.2 --- Comparison between the Badminton Players in the Hong Kong Team and the Hong Kong National Junior Team --- p.105 / Chapter 5 --- Discussion --- p.111 / Chapter 5.1 --- General discussion of the design of the study --- p.111 / Chapter 5.1.1 --- Subject --- p.111 / Chapter 5.1.2 --- Specific test --- p.112 / Chapter 5.1.3 --- Warming up --- p.112 / Chapter 5.1.4 --- Testing protocol --- p.113 / Chapter 5.2 --- Part One --- p.116 / Chapter 5.2.1 --- Test-retest reliability --- p.117 / Chapter 5.2.2 --- Correlation between the PTR and the ASMSTR --- p.120 / Chapter 5.3 --- Part two --- p.122 / Chapter 5.3.1 --- Comparison between the HKT and the non- athletes --- p.123 / Chapter 5.3.2 --- Presentation of torque ratio in the HKJ --- p.133 / Chapter 5.3.3 --- Performance in those with history of shoulder problem --- p.134 / Chapter 5.4 --- Clinical application and suggestion for further study --- p.139 / Chapter 6 --- Conclusion --- p.144 / Chapter 7 --- Reference --- p.146 / Chapter 8 --- Appendix

Para atividade isométrica há relativamente pouca fundamentação na literatura que aborde o contexto de sua variação em função da contração muscular. Assim, este trabalho buscou estudar exercícios isométricos realizados de formas distintas, com o objetivo de verificar variações na atividade mioelétrica. No exercício denominado dissipativo, a contração voluntária é realizada contra um fio inextensível, e no conservativo, a mesma carga é sustentada segurando um peso. Este estudo demonstrou experimentalmente que os sinais de eletromiografia de superfície são diferentes em função do tipo de força isométrica contra a qual o músculo contrai. Os resultados mostram que as diferenças entre os exercícios dissipativo e conservativo dependem do nível de força utilizado, sendo maior em níveis elevados. Os resultados levam a supor que a diferença está associada ao padrão de ativação muscular e ao tipo de fibra muscular recrutada de forma predominante, durante a execução de uma ou outra atividade. De maneira geral, as análises permitem inferir que os exercícios dissipativos apresentam maior ativação muscular e maior ativação de fibras de contração lenta. Já o conservativo, apresenta menor ativação muscular e maior ativação de fibras de contração rápida. As diferenças obtidas foram confirmadas pelas técnicas de visualização denominadas coordenadas paralelas e Viz3D. Estas apresentaram grande potencialidade para o estudo destes sinais, por possibilitar incluir os parâmetros de diferentes sujeitos e músculos como atributos dos exercícios, resultando numa avaliação globalizada. Isso permitiu afirmar que os exercícios apresentam características diferentes. / There are few studies about isometric activity at the literature that approaches the context of his variation in function of the muscle contraction. The aim of the present study is an evaluation of isometric exercises in different ways, analyzing variations at mioelectric activity. In the exercise named dissipative, the voluntary contraction pulls an inextensible wire, whereas in the exercise named conservative the same load is pulled by lifting weights. This study showed experimentally that the electromyography signals are different in function of the two kind of isometric exercises. The results show that the differences among the dissipative and conservative exercises depend on the level of force used, being larger in high levels. These results may be related to the different pattern of muscular activation and the muscular fiber type. The dissipative exercises show a larger muscular activation and larger activation of fibers of slow contraction, whereas the conservative have smaller muscular activation and larger activation of fast contraction fibers. The obtained differences were confirmed by the visualization techniques denominated parallel coordinates and Viz3D. These kind of analyses presented great potentiality for the study of these signals, making possible to include the parameters of subjects and muscles differences as exercises attributes, possibly a global evaluation. The conclusion of this work is that these two isometric exercises present different characteristics.

Para atividade isométrica há relativamente pouca fundamentação na literatura que aborde o contexto de sua variação em função da contração muscular. Assim, este trabalho buscou estudar exercícios isométricos realizados de formas distintas, com o objetivo de verificar variações na atividade mioelétrica. No exercício denominado dissipativo, a contração voluntária é realizada contra um fio inextensível, e no conservativo, a mesma carga é sustentada segurando um peso. Este estudo demonstrou experimentalmente que os sinais de eletromiografia de superfície são diferentes em função do tipo de força isométrica contra a qual o músculo contrai. Os resultados mostram que as diferenças entre os exercícios dissipativo e conservativo dependem do nível de força utilizado, sendo maior em níveis elevados. Os resultados levam a supor que a diferença está associada ao padrão de ativação muscular e ao tipo de fibra muscular recrutada de forma predominante, durante a execução de uma ou outra atividade. De maneira geral, as análises permitem inferir que os exercícios dissipativos apresentam maior ativação muscular e maior ativação de fibras de contração lenta. Já o conservativo, apresenta menor ativação muscular e maior ativação de fibras de contração rápida. As diferenças obtidas foram confirmadas pelas técnicas de visualização denominadas coordenadas paralelas e Viz3D. Estas apresentaram grande potencialidade para o estudo destes sinais, por possibilitar incluir os parâmetros de diferentes sujeitos e músculos como atributos dos exercícios, resultando numa avaliação globalizada. Isso permitiu afirmar que os exercícios apresentam características diferentes. / There are few studies about isometric activity at the literature that approaches the context of his variation in function of the muscle contraction. The aim of the present study is an evaluation of isometric exercises in different ways, analyzing variations at mioelectric activity. In the exercise named dissipative, the voluntary contraction pulls an inextensible wire, whereas in the exercise named conservative the same load is pulled by lifting weights. This study showed experimentally that the electromyography signals are different in function of the two kind of isometric exercises. The results show that the differences among the dissipative and conservative exercises depend on the level of force used, being larger in high levels. These results may be related to the different pattern of muscular activation and the muscular fiber type. The dissipative exercises show a larger muscular activation and larger activation of fibers of slow contraction, whereas the conservative have smaller muscular activation and larger activation of fast contraction fibers. The obtained differences were confirmed by the visualization techniques denominated parallel coordinates and Viz3D. These kind of analyses presented great potentiality for the study of these signals, making possible to include the parameters of subjects and muscles differences as exercises attributes, possibly a global evaluation. The conclusion of this work is that these two isometric exercises present different characteristics.

The development of localized muscle fatigue has classically been described by the nonlinear intensity - endurance time (ET) curve (Rohmert, 1960; El Ahrache et al., 2006). These empirical intensity-ET relationships have been well-documented and vary between joint regions. Xia and Frey Law (2008) previously proposed a three-compartment biophysical fatigue model, consisting of compartments (i.e. states) for active (MA), fatigued (MF), and resting (MR) muscle, to predict the decay and recovery of muscle force. However the model had yet to be validated for static or intermittent isometric tasks. The purpose of this thesis was to provide validation to the biophysical model. The first goal of this thesis was to determine optimal model parameter values, fatigue (F) and recovery (R), which define the "flow rate" between muscle states and to evaluate the model's accuracy for estimating expected intensity - ET curves. Using a grid-search approach with modified Monte Carlo simulations, over 1 million F and R permutations were used to predict the maximum ET for sustained isometric tasks at 9 intensities ranging from 10 - 90% of maximum in 10% increments (over 9 million simulations total). Optimal F and R values ranged from 0.00589 (Fankle) and 0.0182 (Rankle) to 0.00058 (Fshoulder) and 0.00168 (Rshoulder) , reproducing the intensity-ET curves with low mean RMS errors: shoulder (2.7s), hand/grip (5.6s), knee (6.7s), trunk (9.3s), elbow (9.9s), and ankle (11.2s). Testing the model at different task intensities (15 - 95% maximum in 10% increments) produced slightly higher errors, but largely within the 95% prediction intervals expected for the intensity-ET curves. The second goal of this thesis was to conduct a meta-analysis of available percent torque decline data as a function of duty cycle and intensity from literature. For comparison across studies, decay in MVC (% decline) was extracted at a selected range of time points: 30, 60, 90, and 120 seconds across all joints (shoulder, hand/grip, knee, trunk, elbow, and ankle). Searches of the following databases were performed: PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Web of Knowledge, and Google Scholar. The inclusion criteria included: studies with healthy human subjects, ages between 18-55 years old, intermittent tasks with force/torque data, a task time of at least 30 seconds, and published in English. Exclusion criteria included: dynamic contractions, simultaneous multi-joint testing (e.g. squat lifts), functional tasks, body/limb weight as primary resistance, and electrically stimulated contractions. The database search strategy resulted in a total of 2781 potential publications. Of these articles 44 met the required inclusion and exclusion criteria. Since there were so few publications that fit the required inclusion and exclusion criteria, static fatigue papers that were used in (Frey Law and Avin, 2010) meta-analysis and fit the inclusion requirements for this study were used to fill in points at the extreme of the surface (DC=1). Of the 194 publications that were used in the prior meta-analysis, only 3 fit the required inclusion and exclusion criteria for this analysis, for a total of 47 studies (torque decline was typically the limiting factor). From these 47 studies, empirical % decline models could be developed for the joint regions with 3 or more data points (ankle, knee, elbow, and hand/grip) and a general model for each of the 4 discrete time points. The total sample size for each joint ranged from 125 (elbow) to 306 (hand/grip). The total number of data points for each joint ranged from 28 (elbow) -to 68 (hand/grip) with a total of 193 data points extracted. The third goal of this thesis was to compare the empirical models developed from the meta-analysis to the predicted surfaces produced by the biophysical model. Each surface was compared to its empirical counterpart qualitatively and quantitatively. Qualitatively the predicted surfaces reasonable resembled the empirical models. Quantitative analysis was performed by calculating the mean RMS and relative errors between the surfaces. The predicted surfaces had reasonably low range of mean RMS errors across each time point: hand/grip (92.66-238s), knee (73.60-186.25s), elbow (23.62-96.31s), and ankle (34.02-129.63s). The quantitative analysis also showed that the percent of the data points found by the meta-analysis that fell within the predicted 95% confidence interval was reasonably high: 52%(hand/grip; 120s) to 100% (elbow; 60, 90, & 120s). This thesis concluded that this three-compartment fatigue model can be used to accurately represent joint-specific static intensity-ET curves and 3D surfaces of percent torque decline as a function of intensity and duty cycle for short intermittent tasks (i.e. <120 seconds). While the intensity-ET curves are currently used for ergonomics analysis. The relative torque decline surfaces for intermittent tasks that were developed in this thesis provide further insight into what occurs at the muscle level (i.e. decline in muscle force production) during intermittent work cycles. This insight could provide a new method for developing rest-work cycles or job rotation cycles in industry.

<p>Abstract </p><p>The core is the center of gravity in our body. Injuries and overload in the joints, is the most common reason for not be able to work in Sweden today. A god strength capacity in the core is important for secure and effective movements, as well for active athletes, as for non athletes. The increased number of employees, who report in sick today, has been correlated with psychological bad health. New methods to deal with mental and physical health problems among people can indicate to the fact that Yoga in the western world has increased its members, due its spiritual and physical recognition in favor of well being. The purpose with this study was to examine the effect of yoga practice on isometrics muscular strength endurance in the core, and if the mental and physical general health has been effected after 8 weeks of yoga classes twice a week. The method has a quantitative and qualitative approach. Fourteen health female subjects, ranging in age from 32 to 60 years old, were studied. The subjects were evaluated before and after the training program in three test positions for core isometric endurance. There was improvement for all the subjects, in all three tests positions together. The subject’s isometric endurance average improved with 29 %. All subjects reported improvement in physical and mental function after the yogic practices. These findings indicate that regular yoga practice can elicit improvements in isometric endurance in the core, and facilitate mental and physical well being for the subjects.</p>

Current knowledge indicates that nonthermal muscle metaboreflex activity plays a critical role in the modulation of skin vasodilation and sweating. However, the mechanisms of control have primarily been studied during isometric handgrip exercise in which muscle metaboreceptor activation is induced by a brief post-exercise ischemia of the upper limb. While the reflex increase in mean arterial pressure associated with this period of ischemia is consistent with the activation of muscle metaboreceptors, the change in baroreflex activity may in itself modulate the response. Thus, we sought to understand how these nonthermal stimuli interact in modulating the control of skin perfusion and sweating under conditions of elevated hyperthermia. Furthermore, we examined the mechanisms responsible for the maintenance of arterial blood pressure under varying levels of heat stress during isometric handgrip exercise. Our study findings indicate that the parallel activation of muscle metaboreceptors and baroreceptors during post-exercise ischemia causes divergent influences on the control of skin blood flow and sweating; and these nonthermal stimuli are dependent on the level of hyperthermia. Moreover, we report that heat stress reduces the increase in arterial blood pressure during isometric handgrip exercise and this attenuation is attributed to a blunted increase in peripheral resistance, since cardiac output increased to similar levels for all heat stress conditions. These results provide important insight and understanding into the role of muscle metabo- and baroreflex activity on the control of skin blood flow and sweating; along with further knowledge into the cardiovascular mechanisms responsible for the regulation of arterial blood pressure during hyperthermia.