space cognize capacity. Consist with our previous research , the increasing central time represented a high-stress state and anxiolytic-like behavior of rodent, which has also been relieved by CEO. Locomotor activity was composed by horizontal activity and vertical activity. It has been re- ported that physical fatigue could decrease locomotor ac- tivity , unfortunately, few literature reported the changes in locomotor activity during centralfatigue. The measures of horizontal activity in this study composing total distance travelled, number of crossing squares, max- imum distance travelled, and the mean velocity, it is showed a significant increase in CSD rats, and a decreas- ing trend after inhalation treatment without statistical sig- nificance. We hypothesized this result can reflect a high-stress state in CSD rats, accompanying by fear and ir- ritability, and the relaxing property of compound essential oil attenuated these behavioral changings. Similarly, the two parameters of vertical activity in CSD, namely the number and total time of vertical activity, exhibited an evi- dent enhancement, which were decreased in CEO group, implying the antianxiety action of inhalation treatment. Grooming behavior and defecation also reflect anxiety, in this study, a reduction of grooming was seen in CSD group, and CEO improved the grooming occurrence with- out significance. Although there was a slight, non-significant decrease in CEO group of grooming time, we consider this could be ignored. An evident increase of defecation number was observed in CSD group during the test, meanwhile an obvious decrease was showed in CEO group, both suggesting an improvement of essential oil in stress, fear and anxiety.
Many scientists have investigated the changes in brain activity caused by cycling (Comani et al., 2013). Brain activity is changed by altering functional properties in response to demands, using the central governor model and the homeostasis phenomenon (Inzlicht & Marcora, 2016; Noakes, 1997; Noakes, 2000; Noakes, 2012). The evaluation of the patterns of neural response of the cere- bral cortex (neuroplasticity) (Budde, Wegner, Soya, Re- hage, & McMorris, 2016) during intervals with fatigue contributes to a new insight into functional connectivity between different parts of brain activity in HIIT (Taylor & Gandevia, 2008; Taylor, et al., 2016; Comani et al., 2013; Gotshall, Bauer, & Fahrner, 1996). We hypoth- esized in the present study that neural response patterns induced by the centralfatigue in the cortical area are changed by increasing the intensity of training. There- fore, this research aimed to evaluate the effects of centralfatigue during high-intensity pedaling with intermittent changes on brain activity. These changes are done by altering functional properties, which results in spectral power frequencies of brainwaves.
fatigue. We also assessed changes in motor performance and accuracy by computing trial-averaged values of the following outcomes for the first, middle and last 20 trials: (v) average normalized (to MVC) force amplitude during the plateau phase of the contraction (between time 0.5 s and 2 s from contraction onset as defined above corresponding to early static contraction phase after the force reached the target); (vi) average normalized (to MVC) force area within the force curve; and (vii) average force slope during ascending and descending phases of the force curve as a measure of contraction and relaxation speed. The slope was computed by first applying a zero-phase 4 th order Butterworth 10 Hz low pass filter to the force and then, measuring the maximum of 2 nd order polynomial fit of the bell-shaped maximum of the absolute force derivative during the ascending and descending phases of the force curve.
Abstract: Athletes are exposed to high-intensity loads to promote athletic performance, however without appropriate evaluation for its effects. This study investigates the effects of four types of exhaustion exercises on Heart Rate Variability (HRV) and Poincaré features as markers of centralfatigue; Creatine Kinase (CK) and blood lactate concentrations ([LA-]b) as biomarkers of peripheral fatigue. To achieve this purpose, ten healthy volunteers were exposed to exhaustive exercise using isotonic-, isometric-, aerobic-, and anaerobic-fatigue protocols. HRV Poincaré features, standard deviation of instantaneous beat-to-beat R-R interval variability (SD1) and standard deviation of continuous long-term R-R interval variability (SD2) variables were collected. Centralfatigue was tested through the sympathetic stress index (SS) and the sympathetic and parasympathetic index (SS/SD1). Blood samples were collected at the beginning and at the end of the exercises to determine CK and [LA-]b. The SD1 decreased in each exercise protocol, while the SS and SS/SD1 increased. [LA-]b and CK increased at the end of each protocol and correlated with SD1 and SS/SD1. HRV, CK, and [LA - ] b are acute markers to detect, both central and peripheral fatigue; sensitive to the type,
The joint analysis of EMG measures , the positive trend of RMS and negative trend of MPF change, indi- cate a fatigued state for the obese individuals. In con- trast, the negative trends of RMS and MPF change indicate a force decreasing state for the non-obese group, which suggests that they stopped the endurance task prior to a fatigued state. The fatigue state of the middle deltoid of the obese individuals was diagnosed as the result of central rather than peripheral fatigue in this study. This was found from a greater reduction from pre- to post- CAR, which indicated a greater reduction in the ability of the obese group to voluntarily activate their available motor units once they fatigued. Similarly, reduced motor unit activation with obesity was reported for knee extensor [29, 30] and ankle dorsiflexor  muscles suggesting a greater role of centralfatigue with obesity for the lower extremities. Centralfatigue impair- ment with obesity reported for the lower extremities was verified for the middle deltoid muscle in this study.
In addition to enduring muscle weakness, stroke survivors may experience increased susceptibility to muscle fatigue. Both central and peripheral factors can contribute to the overall manifestation of fatigue, which can be defined as a transient exercise-induced reduction in the force-generating capacity of muscle (Bigland-Ritchie and Woods, 1984). The few studies that have investigated fatigue in stroke survivors during voluntary contractions have reported relatively higher centralfatigue on the affected side when compared to the less-affected side and healthy controls (Riley and Bilodeau, 2002; Knorr et al., 2011). Centralfatigue encompasses both decreases in descending motor commands to spinal motoneurons, and reduced excitatory afferent input, as well as decreases in motoneuron responsiveness due to changes in intrinsic properties or inhibitory afferent input (Gandevia, 2001). Conversely, in these studies stroke survivors showed lower levels of peripheral fatigue on the affected side. Peripheral fatigue refers to changes occurring beyond the motoneuron, including changes within the muscle fibers. Centralfatigue was assessed in the stroke studies using twitch interpolation to quantify voluntary muscle activation (Riley and Bilodeau, 2002; Knorr et al., 2011), and peripheral fatigue was evaluated using the compression of the surface EMG power spectrum (Svantesson et al., 1999; Riley and Bilodeau, 2002) and changes in maximal twitch torque (Knorr et al., 2011).
Central DA synthesis and metabolism have been shown to be enhanced in several brain regions during exercise (Foley and Fleshner, 2008). Meeusen et al. (1997) showed that 60 min of exercise significantly increased DA content in the striatum. Increased DA concentrations have also been observed in the hypothalamus and hippocampus during exercise (Chaouloff, 1989). We found a similar increase in DA levels from striatal homogenates of rats in both normoxic and hypoxic conditions after a bout of exhaustive swimming, which suggests an enhanced synthesis of DA. In addition, pharmacological experiments demonstrated that either stimulation of DA release with amphetamine or inhibition of DA reuptake with bupropion could significantly improve exercise performance (Bhagat and Wheeler, 1973), and thus testified to a potent effect of functional DA release on the delay of fatigue. We found that striatal DOPAC, a metabolite of DA, was elevated in rats after exhaustive swimming under normoxic conditions, which indicates an elevated metabolism of DA and its functional release. This result is consistent with the evidence of an increased concentration of striatal DA in treadmill-running, exhausted rats (Heyes et al., 1988). However, the elevation of DOPAC induced by exhaustive exercise was blunted by severe hypoxia exposure, which reflected a poor DA release of exhausted rats in hypoxia. Together, these results imply that exhaustive-swimming-induced centralfatigue is more severe in hypoxic than in normoxic rats.
The results of the multiple logistic regression analysis showed that patients who are more physically active are less likely to be classified as CFS. The amount of sleep per night was not a significant determinant. With regard to illness rep- resentations, the results showed that patients who believed that their fatigue was associated with more severe conse- quences, that it would last for a longer period of time, and patients who attributed more additional symptoms to their condition were more likely to be classified as CFS, a finding that is similar to other studies [9, 16]. Finally, patients who reported lower levels of Ball or nothing behavior^ were more likely to have a CFS diagnosis. This finding may suggest that B all-or-nothing ^ behavior is more characteristic of the earlier stages of fatigue, which is in line with a prospective cohort study , demonstrating that, within a patient cohort suffer- ing from an acute viral infection, B all-or-nothing ^ behavior was a strong predictor of the development of CFS over time.
Examination of the state of the art shows that an efficient way to improve the strain based approach’s accuracy in estimating fatigue damage in those components weakened by relatively sharp notches may be adopting appropriate elasto-plastic fatigue strength reduction factors . In other words, the detrimental effect of severe stress/strain gradients can directly be accounted for by following a strategy similar to the one proposed by Neuber  and Peterson  to estimate notch fatigue strength in the high-cycle fatigue regime. In this scenario, it is worth mentioning here that Susmel and Taylor  have recently proven that Peterson’s Point Method as well as Neuber’s Line Method can successfully be extended back to the low/medium cycle fatigue regime by simply modelling metallic materials’ cyclic elasto-plastic behaviour explicitly. The main advantage of such a modus operandi is that the critical distance value is no longer dependent on the number of loading cycles to failure as it happens instead when the Theory of Critical Distances (TCD) is applied by post-processing linear-elastic stress fields .
ABSTRACT: Surface roughness is an important parameter that affects the fatigue life/ strength of a material. The effect of surface roughness on the fatigue life of Al 6160 alloy is investigated in the current research. Standard fatigue specimens are fabricated as per the requirement of the 25KN axial fatigue testing machine and tested for low cycle fatigue life. Specimens of three categories are tested for the fatigue life and the results are compared. Firstly, smooth specimen as per the standard is tested, followed by specimen with first grade of roughness, followed by the specimen with second grade of roughness. It is clearly evident from the test results that, as the surface roughness increases, the fatigue life decreases drastically.
Abstract : The paper is mainly to make a fast fatigue life prediction for aluminum alloy 5754welding spot. A large number offatigue tests for aluminum alloy 5754 show that the fatigue failure of welding spot is mainly caused by the defects of welding process, so the welding spot defect have a big impact on the fatigue life prediction for welded parts.Based on the experimental data to match an S - N curve fitting of the aluminum alloy5754. Simulation analysis in the workbench—an finite element software can find the maximum stress, and predictthe minimum lifeof aluminum alloy material by using the S-N curve.At the same time, compared with the life of welding partswith the defects, getthe importance of welding defects for parts life influence.
Five (5) out of 17 subjects reported some adverse symptoms including flatulence and discomfort, which has been previously reported with FOS use at much higher doses . In contrast, other subjects in this study reported benefits including reduced bowel irrita- tion and GIT improvement which may be associated with the potential enhancement of bifidobacteria which have been reported to be mediated by FOS . The symptom questionnaires and urine excretion data for these five subjects were further evaluated in comparison to the remaining 12 subjects to see whether any issues of sub-health might be identified as markers of individ- uals likely to experience GIT discomfort on supplemen- tation. The 86-item symptom questionnaire enabled the evaluation of symptom groups or indices including a broadly based “neurological” index. This index included assessments of the following symptoms reported in the prior 7 days: faintness or dizziness; crying easily; tinnitus; photophobia; mind going blank; trouble concentrating; hypersensitivity; mental fatigue; and panic attacks. The mean neurological index score for the 5 subjects reporting the adverse GIT symptoms, was significantly higher prior Table 2 Types and number of comments regarding
Fifteen patients with SMA type 2 (n = 8), type 3a (n = 5) and type 3b (n = 3) aged 10–49 and with a broad range in clinical severity (Hammersmith Functional Motor Scale Expanded score = 0–66) (Table 4) performed 1,2 or 3 of the endurance shuttle tests (i.e. ESNHPT, ESBBT, ESWT) tests depending on their level of motor function. The comprehensibility, acceptability and measurement completion of all three tests were excellent despite mod- erate to severe self-reported muscle fatigue. All subjects were strongly motivated to perform well on the test and willing to do the test again in the context of future stud- ies. Beforehand, it was expected that at least 50% of the subjects would end the test prematurely because of fatig- ability. Although most subjects did show signs of fatig- ability at the end of the test reflected by decrease in coordination, compensatory movements and perceived exertion, the drop –out rate was lower than expected on the ESNHPT (31%), ESBBT (45%) and ESWT (50%). The ESWT showed a trend towards ceiling effect (Tlim (Mn) = 462/600 s). It was observed that during the ESBBT subjects were actively compensating for fatigabil- ity by leaning on the box.
Teachers are entrusted with the responsibility to educate the future leaders of tomorrow and are essential to student achievement (Murphy, Delli, & Edwards, 2004). Moreover, they are challenged with the task of successfully performing many different roles and responsibilities in their every day work, including: being a motivator, manager, observer, counsellor (Cohen, Manion, & Morrison, 1996), school leader, resource provider, mentor for fellow teachers, and an active agent of change of themselves and their students (Harrison & Killion, 2007), among others. Although commonly construed as an "easy" occupation, Johnson et al. (2005) found teaching to be one of the most stressful professions with similar levels of stress to those of paramedics, police officers, and social service workers. With the large number of roles and responsibilities teachers face, it is no wonder that two distinct concepts have been linked to reduced emotional and physical well-being in teachers; those concepts being burnout (Burke & Greenglass, 1995) and more recently compassion fatigue, also referred to as secondary traumatic stress (STS; Hatcher, Bride, Oh, King, & Catrett, 2011). With the limited amount of literature on compassion fatigue in teachers (Borntrager et al., 2012), and the prevalent issue of burnout in teachers, the present study will provide: a review of the relevant research literature; offer a theoretical framework to develop a comprehensive understanding of teacher burnout and compassion fatigue; describe the positive impact of professional development on burnout and compassion fatigue; and finally, describe a relevant professional development opportunity for teachers and evaluate the effectiveness of the program in both the short term and after 6 months with the goal of improving teacher well- being, enhancing the quality of student education, and adding to the academic literature.
Objective: To observe prevalence of depression and sleep disturbances in multiple sclerosis (MS) patients and their correlation with associated fatigue. Study Design and Setting: Prospective observation study in a university tertiary research hospital in India. Materials and Methods: Thirty‑one patients (6 male and 25 female) with definite MS (McDonald’s criteria) presented in out‑patient/admitted in the department of neurology (between February 2010 and December 2011) were included in the study. Depression was assessed using Beck’s Depression Inventory (BDI). Sleep quality was assessed using Pittsburg Sleep Quality Index (PSQI). Disease severity was evaluated using the Kurtzke’s expanded disability status scale (EDSS). Fatigue was assessed using Krupp’s fatigue severity scale (FSS). We tried to observe correlation of depression and sleep disturbance with associated fatigue in MS patients. Results: The age of patients varied between 16 and 50 years (30.1 ± 9.1). The mean age at first symptom was 25.2 ± 6.4 years (range 14‑39 years). The prevalence of sleep disturbance and depression was 51.6% (16/31) each and fatigue 58.1% (18/31) in the study group. The PSQI scores were significantly greater in the patients with fatigue as compared with those without fatigue indicating poorer sleep quality is associated with fatigue in MS (P = 0.005). The BDI scores were also significantly higher in the fatigue group showing that severity of depression also strongly correlated with fatigue (P = 0.001). Conclusions: Depression and sleep disturbance in patients with MS is significantly correlated with associated fatigue.
Fatigue tests were performed on a MTS 810 servo-hydraulic machine under a total strain-controlled triangular wave loading mode. Six straining ratios (R ε ) of –1, –0.52, –0.22, 0.029, 0.18, and 0.48 were employed. In order to avoid the influence of strain rate, a constant strain rate of 4 10 –4 s –1 was used. An maximum likelihood statistical principle was applied in the test. The method is based on the maximum likelihood fatigue test method (MLFTM) (Nakazawa and Kodama, 1987), which makes it possible to estimate the probabilistic stress-life (S-N) curves with smaller size of specimens with classical maximum likelihood method (MLM) (Ling and Pan, 1997). An so-called general MLM proposed by Zhao-Gao-Wang (2001) helps to overcome the limitation of the classical MLM (Zhao, Wang and Gao, 2001), and can be used in the estimation of both S-N relations, σ-ε relations and ε-N relations. Therefore, from saving the size of specimens and making the most of test information, an improved test method including the properties of general MLM was proposed in the test and extrapolated the MLFTM into the fields of strain-controlled tests. Details can be explained as follows:
The present paper addresses the problem of estimating fatigue strength of welded joints when the weld seams are inclined with respect to the direction of the axial cyclic loading being applied. From a fatigue design point of view, the main complexity lies in the fact that, with this particular welded geometries, although the applied loading is uniaxial, accurate fatigue assessment can be performed provided that the degree of multiaxiality of the nominal/structural/local stress states at the weld toes/roots is modelled effectively. To this end, in the present investigation the Modified Wöhler Curve Method (MWCM) is attempted to be used to assess the fatigue strength of steel joints with inclined welds by using this multiaxial fatigue criterion in conjunction with nominal stresses, hot-spot stresses, effective notch stresses, and the Theory of Critical Distances (TCD). A large number of experimental results taken from the literature and generated by testing inclined fillet welds was used to check the accuracy and reliability of the MWCM applied along with these different ways of determining the relevant stress states. The results obtained from this validation exercise demonstrate that the MWCM returns satisfactory estimates when it is used to assess fatigue strength in the presence of inclined welds, with this holding true independently of the specific stress analysis strategy being adopted.
Evaluation of the results from a preliminary experimental study with Resin Injected Bolted Joints (RIBJs) for pultruded Fibre Reinforced Polymer (FRP) materials has shown that this connection method is slip and fatigue resistant. The investigation used three loading procedures for both static and cyclic fatigue. Static strength tests were performed with standard bolted connections to provide baseline joint strengths. Static creep and fatigue tests with injection bolted connections were conducted to establish joint response for two epoxy resins that have properties for injected bolts. The test series had the two steel bolt sizes of M16 and M20, and used available pultruded FRP materials for cover and inner plates. Using a double lap shear joint configuration, 46 joints (or twenty-three specimens) were characterised using a modified test methodology based on guidance in annexes in BS EN 1090-2:2008. Differences in the loading procedures from the standard should not have influenced the outcomes reported in this paper.